                          RAMSOFT proudly presents:

           -------------------------------------------------------
            D I S C i P L E / + D   T E C H N I C A L   G U I D E 
           -------------------------------------------------------

                          Revision 8 (09 Sept 1999)


                                SUMMARY:
                                ========

                     1 ..... DISCiPLE/+D general features
                     2 ..... Memory layout
                     3 ..... I/O ports
                     3.1 ... DISCiPLE port 7Bh (123 dec.)
                     4 ..... UFIA layout
                     5 ..... System calls (hook codes)
                     5.1 ... Internal system calls
                     5.2 ... Programming example: loading a file
                     6 ..... Disk layout
                     7 ..... Filesystem details
                     8 ..... File types table
                     9 ..... GDOS/G+DOS extended BASIC commands
                     9.1 ... The network
                     9.2 ... The snapshot button
                     9.3 ... GDOS/G+DOS and UNIDOS error messages
                    10 ..... GDOS/G+DOS and UNIDOS system variables
                    11 ..... UNIDOS extended BASIC commands
                    12 ..... Connectors pinouts
                    12.1 ... Connecting a PC 5.25" drive
                    13 ..... VL1772 FDC programming info
                    14 ..... Credits and contact info



DISCLAIMER
==========

Although we have tried to be very accurate, this document may contain some
errors. The authors do not assume any responsability for any loss and/or
damage directly or indirectly caused to your system by use of any information
reported here.
See the credits at the end of the document on how to contact the authors.



FOREWORDS
=========

We (Ramsoft) have been using the DISCiPLE interface for a long time and
we have appreciated all the power of this disk system. We have spent many
hours trying to understand the smallest details to make full use of its
capabilites, and a lot still has to be known.
Now we have decided to release all the info we collected mostly ourselves,
in the hope that it may be useful to anybody and that it will encourage
the developement of new programs and products for this wonderful system.



COMMON TERMS
============

  DRAM - The sector buffer.
   RPT - A system variable which points to a byte in the DRAM.
  UFIA - User File Information Area, a 24 byte structure which describes
         a file for system calls.
  DFCA - Disk File Channel Area.



1. DISCiPLE / +D features
=========================
  
     8 KB EPROM (for disk BIOS)
     8 KB RAM
     NMI magic button (snapshot)
     Parallel port (not bi-directional)
     Floppy disk port (controlled by VL1772 FDC)
     High speed disk operations: load 128K in less than 7 seconds.

 DISCiPLE only features:

     Two ATARI joystick ports (Sinclair 1, Sinclair 2 / Kempston)
     Two network connectors (Interface 1 compatible, 3.5mm mono jack)
     Inhibit button (to lock out the interface)
     Throughout bus connector (to plug in other devices)

 


2. MEMORY LAYOUT
================

When the interface memory is paged in (see below), the first 16K of the
Z80 address space have this mapping:

  Address   DISCiPLE GDOS   DISCiPLE UNIDOS   +D
  --------------------------------------------------
   0x0000   8K RAM          8K ROM            8K ROM
   0x2000   8K ROM          8K RAM            8K RAM

So, UNI-DOS memory mapping is the same as +D, even on DISCiPLE.
Read [3.1] to see how it is possible to swap ROM/RAM addresses on the
DISCiPLE.





3. DISCiPLE and PlusD I/O PORTS
===============================

NOTE: Joystick 1 is both Kempston (port 1Fh) and Sinclair 2 (keys 6,7,8,9,0)
      Joystick 2 is Sinclair 1 (keys 1,2,3,4,5)
      Network is an Interface 1 compatible net.

 DISCiPLE I/O ports:

 Port  In              Out                       Notes
 ---------------------------------------------------------------------------
  1Bh  FDC status      FDC command               See also section 13
  5Bh  track register  track
  9Bh  sector regist.  sector register
  DBh  data register   data register

  1Fh  Joystick 1      control:
       b0 right        drive select
       b1 left         side select
       b2 down         single/double density
       b3 up           ROM bank select
       b4 fire         Inhibit switch control    
       b5  --          ext. select (?)
       b6 PRN BUSY     printer STROBE
       b7 network      network

  3Bh     --           wait when net=1           (*)
  7Bh  set boot        reset boot                see [3.1]
  BBh  mem. page in    memory page out           (**)
  FBh     --           printer data
  FEh  Joystick 2                                scanned as Sinclair joy.

(*) Port 3Bh is used for network synchronization (same as bit 5 of Interface
    One's port EFh). Any OUT to port 3Bh will halt the Spectrum until the
    logic level on the network is 0. It is used to wait for the start bit
    of a transmission frame.
    The network bus carries TTL logic levels (0 = 0 Volts, 1 = 5 Volts).
    The bit rate is 87.5 Kbps and data are exchanged in packets of 256 bytes
    max using a simple data-link level protocol.


 PlusD I/O ports:

 Port  In              Out                       Notes
 ---------------------------------------------------------------------------
  E3h  FDC status      FDC command               See also section 13
  EBh  track register  track
  F3h  sector regist.  sector register
  FBh  data register   data register

  EFh  b0/b1 --        drive select
       b2    --        single/double density
       b3    --        ROM bank select
       b4    --          --    
       b5    --        ext. select (?)
       b6    --        printer STROBE
       b7    --        side select

  E7h  mem. page in    memory page out           (**)

  F7h  b0/b6 --        printer data (8 bits)
       b7 PRN BUSY     

(**) DISCiPLE and +D memories are also paged in whenever the Z80 fetches an 
     instruction from the following addresses:

     0x0000, 0x0008, 0x0066, 0x028E.






3.1 DISCiPLE PORT 7Bh AND MEMORY ADDRESSES
==========================================

Port 7Bh (123 decimal) is available only on the DISCiPLE and has a flip flop 
attached to it. It can be used to swap the RAM/ROM addresses in this way:

Access  ROM      RAM      Purpose
----------------------------------
  IN    0x0000   0x2000   reset ff
 OUT    0x2000   0x0000   set ff

This feature is used by GDOS to know if it necessary to load the system
file from disk on boot or after two consecutive resets without any DOS
command between them; UNIDOS ignores this feature, so any swap attempt will
result in a system crash.

In GDOS there is a variable located in RAM at offset 0x1DE4 that is set to
0x44 ('D') after a BASIC syntax check (i.e. after a RST 08h with a code lower
than 1Bh) and after a bootstrap: this variable indicates that the DOS services
have been called almost once. Whenever the user resets the computer, the flip
flop attached to port 7Bh is reset, so the ROM will be placed at 0x0000. When
the first interrupt occurs, the keyboard scanning routine is called at 0x028E
and the DISCiPLE memory is automatically paged in. At offset 0x028E in the
DISCiPLE's ROM there's a routine that checks if the variable we said above
holds 0x44: if it's the case, then the same routine puts 00h in there to say
that DOS services haven't been called since last reset; otherwise the routine
sets the variable to 0x53 ('S') and copies the first 2335 (0x091F) bytes of
ROM in the RAM: in this case the system file has to be loaded again.
When all is finished, the memories will be swapped again (i.e. the flip flop
will be set) by OUTing to port 7Bh, the DISCiPLE paged out by OUTing to port
BBh and the keyscan routine is finally executed.

INning from port 7Bh has the same meaning of a system reset for the DOS, so
after reading 2 times from port 7Bh without typing a DOS command between them
the system file needs to be reloaded.

NOTE that since all this is based on the keyscan routine in the Spectrum's
ROM, nothing will happen by INning from port 7Bh if the call is not performed
(i.e. if interrupts are disabled in IM 1 or we're not in IM 1 or keyboard is
scanned in a custom way); however the last operation with port 7Bh must be an
OUT before the routine in the ROM is executed if you want to keep the system
safe by resetting once.




4. USER FILE INFORMATION AREA (UFIA)
====================================

This is a DOS structure often used by the kernel routines and usually pointed
to by the register IX.


   Offset Len   Meaning
   ---------------------------------------
        0   1   Drive number (1, 2 or '*' (2Ah) for current)
        1   1   Program number (in the directory)
        2   1   Stream number
        3   1   Device density type ('d'=DD, 'D'=SD)
        4   1   Directory description (see below)
        5  10   File name (padded with spaces)
        15  1   File type (see below)
        16  2   Length of file
        18  2   Start address
        20  2   Basic length
        22  2   Autostart line




5. SYSTEM CALLS (both DISCiPLE and +D)
======================================

To invoke system services you must use the IF1 protocol:

     RST 8
     DB #service

All the functions return an error code into register A.

IMPORTANT NOTES:
You cannot perform RST 8 calls from within a routine located into the
interface's RAM.
You must not call ROM address 0x028E (keyboard scanning routine) from
within an interrupt routine, since this would crash the Spectrum when a
DISCiPLE/+D is connected; some programs crash due to this fact
(eg SoundTracker v1.1) - you may try to correct the problem replacing the
CALL 0x028E with a RST 0x38.
A few programs (like some games converted to disk) do not use the RST 8
mechanism but make absolute CALLs to the DOS or the BIOS routines instead -
a very bad practice!

This is the list of GDOS3 (G+DOS2) hook codes with input parameters:

Implemented Interface I hook codes:

 CONSIN (1Bh) - Console input
CONSOUT (1Ch) - Console output
 PRTOUT (1Fh) - 
 KBDTST (20h) - 
 SELDRV (21h) - Select drive
 OPTMPM (22h) - 
 CLOSEM (23h) -
  ERASE (24h) -
  RDSEQ (25h) -
  WRREC (26h) -
 OPTMPM (2Bh) -
 DELBUF (2Ch) -
 UNPAGE (31h) - Unpage shadow ROM
   CALL (32h) - Call shadow ROM routine

GDOS3 (G+DOS2) specific hook codes:

  HXFER (33h) - transfer file description and header to the DFCA.
                IX = UFIA address
  OFSM  (34h) - open file sector map with the info in the DFCA.
                The RTP is set to the beginning of the DRAM.
  HOFLE (35h) - open a file.
                IX = UFIA
                Combines the previous two functions.
                Sets the last 9 bytes of UFIA with the file header.
  SBYT  (36h) - Save a byte to DRAM location pointed by RTP.
                A = byte to save.
                If the sector buffer is full, it is automatically saved
                to disk.
  HSVBK (37h) - Save a block of data.
                DE = start address of data.
                BC = number of bytes to save.
  CFSM  (38h) - Close file sector map.
                Flushes DRAM, closes file and updates the directory.
  PNTP  (39h) - Output a byte to the parallel port.
                A = byte to output.
  COPS  (3Ah) - Copy the screen to printer.
  HGFLE (3Bh) - Get a file from disk.
                IX = UFIA
                The first sector is loaded to DRAM and RPT is set to the
                first byte.
  LBYT  (3Ch) - Load the byte pointed by RPT.
                Returns A = byte read.
                If needed, another sector is read from the disk.
                RPT is updated consequently.
  HLDBK (3Dh) - Load a block of data.
                DE = start address (where the data will be put)
                BC = number of bytes to read
  WSAD  (3Eh) - Write the DRAM to a sector in the disk.
                D = track
                E = sector
                RPT is restored to the beginning of DRAM.
  RSAD  (3Fh) - Read a sector to DRAM.
                D = track
                E = sector
                Same as 3Eh.
  REST  (40h) - Reset drive and seek track 0.
                Drive number is specified into the UFIA.
  HERAZ (41h) - Erase the file on disk identified by UFIA.
                IX = UFIA address.
        (42h) - Large screen dump
  PCAT  (43h) - Disk catalogue
                It uses the information in the UFIA. Drive and stream must
                be set up.
                Offset +0Fh of UFIA may contain one of the following:
                  02h for CAT !
                  04h for CAT
                  12h for CAT ! with a filename mask
                  14h for CAT with a filename mask
                The filename must be stored starting at offset +05 of UFIA
                and may contain wildcards.
  HRSAD (44h) - Load sector
                 A = drive number
                 D = track number
                 E = sector number
                IX = Address to load to
  HWSAD (45h) - Save sector
                 A = drive number
                 D = track number
                 E = sector number
                IX = Address to save from
        (46h) - Open and close streams (how?)
  PATCH (47h) - Pages the shadow memory
                Returns HL=0 on DISCiPLE
                        HL=1 on PlusD
                        HL=2 on DiSCDOS

UNIDOS specific hook codes:

        (48h) - Load file
        (49h) - Verify file
        (4Ah) - Merge
        (4Bh) - Save file
        (4Ch) - Open file
        (4Dh) - POINT (see UNIDOS)
        (4Eh) - Flush buffers to disk
        (4Fh) - Close file
        (50h) - Clear channels
        (51h) - Rename file
        (52h) - Move stream
        (53h) - Move file
        (54h) - Select disk and directory




5.1 INTERNAL SYSTEM CALLS (both DISCiPLE and +D)
================================================

Here is the purpose of the RST commands when the DISCiPLE or the +D memories
are paged in.

RST 00h - Reset 
RST 08h - Call system services; the required service code must follow (1)(2)
RST 10h - Call in Spectrum ROM; the routine address must follow (3)
RST 18h - GDOS, G+DOS : reserved (for syntax check)
          Uni-DOS : low-level system services; the required service code must
          follow
RST 20h - Print DOS error report : the error code must follow
RST 28h - Performs a RST 20h in the Spectrum ROM 
RST 30h - Gets interpreter status : Z=0 if checking syntax, Z=1 if executing
RST 38h - Enables interrupts

(1) = ROM 1 must be paged in Spectrum 128K
(2) = The interface is automatically paged in by the hardware
(3) = Be sure that the right Spectrum ROM is paged in





5.2 EXAMPLE: LOADING A FILE.
============================

Here is the simple loader that we have often used in our programs. It will
load a CODE file called "blk0.DF" in memory at its original start address.
This routine will work fine with DISCiPLE, +D and UNIDOS (all versions).
Note: no error checking is done.

          LOAD:  LD   IX,UFIA           ; IX must point to the UFIA
                 RST  08  DB 3B         ; HGFLE: open the file
                 LD   DE,UFIA+0F        ; the file header will be put here
                 LD   B,09              ; the first 9 bytes of the file
         L_HDR:  RST  08  DB 3C         ; LBYT: get a byte from the DRAM
                 LD   (DE),A            ; store the byte
                 INC  DE          
                 DJNZ L_HDR             ; fetch all the 9 bytes
                 LD   DE,(UFIA+10)      ; get the file start address
                 LD   BC,(UFIA+12)      ; get the file length
                 RST  08  DB 3D         ; HLDBK: load the whole block of data
                 RET                    ; finished!

Now the UFIA follows. Only the first 15 bytes must be preset by the user
before calling HGFLE.
The last 9 bytes are overwritten with the 9 bytes header of the file.

UFIA:            DB 01,                 ; drive number ('*' for default)
                    00,
                    00,
                    'd',                
                    04,                 ; file type 04 = CODE
                    "blk0.DF   ",       ; file name (padded with spaces)
UFIA+0F             00,                 ; will contain the ROM-ID
UFIA+10             00, 00,             ; will contain the file address
UFIA+12             00, 00,             ; will contain the file length
                    00,
                    00,
                    00,
                    00

Note that loading address and length are read from the 9 bytes header of
the file itself. To force the file to be loaded at a different address, simply
change the LD DE,(UFIA+10) instruction (e.g. with a direct LD DE,nn).





6. DISK LAYOUT
==============

The disk has 80 tracks of 10 sectors (512 bytes double density, 256 bytes low
density) each, for a total capacity of 800KB (DS/DD).
The first four tracks of the disk (tracks 0-3 side 0) are reserved for the
system and contain the disk directory, leaving 780KB available for user data. 
The directory consists of 80 consecutive file descriptors, each one taking
256 bytes; thus, the descriptor of file #48 resides in the first 256 bytes
of sector 4 track 2.
The directory has a fixed dimension and can only contain up to 80 files.
UNIDOS overcomes this limitation introducing subdirectories and allowing to
specify the maximum number of file entries for each directory.

Disks formatted with DISCiPLE or +D can be read and written by common PC
disk drives and viceversa.





7. FILE DESCRIPTOR FORMAT
=========================

Now we will see the details about a single directory entry.
NOTE: All numbers are in decimal.

General structure:

OFFSET   MEANING
  0      File type (see FILE-TYPES table); 0 = erased (free entry)
 1-10    Filename (padded with spaces)
11-12    Number of sectors occupated by the file (in Motorola byte order)
 13      Track number of the first sector of the file
 14      Sector number of the first sector of the file
15-209   Sector allocation bitmap. Each bit corresponds to a disk sector. 
         A bit is set if the corresponding sector belong to the file.
         Examples: byte 15, bit 0 corresponds to track 4, sector 1; 
         byte 16, bit 3 means track 5, sector 2...
         IMPORTANT NOTE:
         The s.a.b. is used only during saving operations: the s.a.b. of
         all the 80 files are merged together (OR) so that the system
         knows which sectors are free (not allocated to any file).
         During loading a faster method is used: each sector contains
         only 510 bytes of data; the last two bytes contain the
         track number and the sector number of the next sector of the file,
         respectively. The last sector of the chain contains (0,0) as the
         last two bytes.

210-255  Depend on the file type.

BASIC (type 1)
---------------
211      Always 0 (this is the id used in tape header)
212-213  Length
214-215  Memory start address ( PROG when loading - usually 23755)
216-217  Length without variables
218-219  Autostart line
NOTE: These 9 bytes are also the first 9 bytes of the file.

NUMBER ARRAY (type 2)
---------------------
211      Always 1 (this is the id used in taper header)
212-213  Length
214-315  Memory start address.
216-217  Array name, probably ignored.
218-219  Not used
NOTE: These 9 bytes are also the first 9 bytes of the file.

STRING ARRAY (type 3)
---------------------
211      Always 2 (this is the id used in tape header)
212-219  Same as for type 2
NOTE: These 9 bytes are also the first 9 bytes of the file.

CODE FILE (type 4)
------------------
211      Always 3 (this is the id used in tape header)
212-213  Length
214-315  Start address
216-217  Not used
218-219  Autorun address (0 if there is no autorun address)

48K SNAPSHOT (type 5)
---------------------
211-219  Not used
220-255  Z80 registers (in words) in the following order:
         
           IY IX DE' BC' HL' AF' DE BC HL I SP (see below for R and AF)

         Register I is in the MSB of the corrisponding word (byte offset 239),
         so that it is loaded with:

           POP AF
           LD I,A

         The Interrupt Mode is desumed by the value of the I register: if
         it contains 00h or 3Fh then IM1 is assumed, else IM2 is set.
         The IFF2 status (IFF1=IFF2) is retrieved from the P/V bit of the
         flag register F.

         SP is actually SP-6, because the original stack is "corrupted"
         with the following 6 bytes (in ascending order):

           R AF PC  ( ----> decreasing stack )
           |     |
           SP    SP+6 (original SP)

         (R is in the MSB of the corresponding word) so that the return code
         could be something like this (actually it is a bit more complex):

           POP AF
           LD R,A
           POP AF
           RET

MDRV (type 6)
-------------
This is a microdrive cartridge image. Details omitted.
NOTE: UNIDOS mdrv files are completely different from GDOS ones.

SCREEN$ (type 7)
----------------
Same as type 4 with Start=16384 and Length=6912

SPECIAL (type 8)
----------------
211-255  Any meaning assigned by the programmer.

128K SNAPSHOT (type 9)
----------------------
Same as 48K Snapshot. The first byte of the file is a copy of the page
register (port 0x7FFD), usually held in the system variable BANKM (23388).
The 8 RAM pages are saved in ascending order from 0 to 7.

OPENTYPE (type 10)
------------------
210     Number of 64K blocks in the file
211     Always 9 (not sure)
212-213 Length of the last block 
214-255 Not used

NOTE: Opentype files can be more than 64K in length and are usually created
and handled with the stream-related BASIC statements, such as OPEN #, CLOSE #,
PRINT #, INPUT # and so on.
See chapter [9] for a brief description of these statements.

EXECUTE (type 11)
-----------------
210-255 Same as CODE file (type 4), but Length=510 and Start=0x1BD6 implicitly
        (0x3DB6 for +D). The sector is loaded into the interface RAM
        and executed (it should contain relocatable code!).

SUBDIRECTORY (type 12) - UNIDOS
-------------------------------
210-212 Same as Opentype (type 10). This file is always held on contiguous
        sectors. The last two bytes of a sector do not contain the address
        of the next sector. The structure is the same as the root directory,
        but the first entry contains the file header number of the parent
        directory. The last two bytes of the last sector contain 0xFFFF.
213     Capacity (number of file entries allowed).

CREATE (type 13) - UNIDOS
-------------------------
210-255 Same as CODE file but the start address is ignored.





8. FILE-TYPES TABLE
===================

This table lists the various MGT file types with their correspondent ID's.
Where possibile, it is also reported the file type ID used by the standard
Spectrum ROM in the tape header. The ROM-ID is part of the 9 bytes header
of the file (same as bytes 211-219 of the directory entry).

NOTE: under UNIDOS, add 128 for hidden files and 64 for protected files.

Code          Type                   CAT string   ROM-ID
-------------------------------------------------------------
 0            ERASED (free entry)    (NA)         NA
 1            BASIC                  BAS          0
 2            NUMBER ARRAY           D.ARRAY      1
 3            STRING ARRAY           $.ARRAY      2
 4            CODE                   CDE          3
 5            48K SNAPSHOT           SNP 48k      NA
 6            MICRODRIVE             MD.FILE      NA
 7            SCREEN$                SCREEN$      NA
 8            SPECIAL                SPECIAL      NA
 9            128K SNAPSHOT          SNP 128k     NA
10            OPENTYPE               OPENTYPE     NA
11            EXECUTE                EXECUTE      NA
12  (UNIDOS)  SUBDIRECTORY           DIR          NA
13  (UNIDOS)  CREATE                 CREATE       NA





9. GDOS EXTENDED BASIC SYNTAX
=============================

GDOS extends the BASIC to provide support for disk operations.
When you switch the Spectrum on, you must initialize the system; to do so,
insert a disk containing the operating system file ("SYS*" on DISCiPLE and
"+SYS*" for +D) into the first drive and then enter "RUN".
The DOS also looks for the first file called "auto*" and runs it if found.
The "auto*" file is not searched for if the command "RUN boot" is entered.
NOTE: File names are case insensitive and may contain wildcards ('*' and '?').

To show the disk contents, enter:

        CAT 1 (for drive 1)     or
        CAT * (current drive)

You may also enter commands like these:

        CAT 1;"a*"
        CAT #3;1;"sys*"
        CAT 1!
        CAT #3;1!

so you can redirect the CAT output to any channel and you may specify a file 
name which may contain wildcards to show only matching files.
If the command ends with a '!' then an abbreviated catalogue is shown, 
containing just a list of (matching) file names.

To LOAD/SAVE a file:

        LOAD d<dn>;"filename" [CODE|SCREEN$|DATA|etc]
        LOAD p<fn>
        SAVE d<dn>;"program" [CODE|LINE|SCREEN$|etc]

        where <dn> is a drive number (1-2)
              <fn> is a file number (1-80)

You must specify 'S' to load a 48K snapshot and 'K' for a 128K snapshot.
Case of letters 'S' and 'K' is important.

Examples:

 LOAD d1;"screen" SCREEN$
 LOAD d*;"pippo"             loads program pippo from the current drive
 LOAD d1;"snap128"K          loads the 128K snapshot 'snap128'
 SAVE d2;"rom" CODE 0,16384  this saves the DISCiPLE memory!

Note: "d1" with lowcase 'd' refers to DS DD disks (80 tracks double sided);
in ROM version 3 the only difference seems to be that if you use 'D' a CAT
command is also performed after the operation.
Early versions of the OS used "D1" (capital 'D') for single sided disks.
This applies always when you have to specify the 'd<dn>' field.
Please use only DS/DD disks.

When saving CODE files, an autostart address can be specified as a third
parameter:

 SAVE d*;"runme" CODE 32768, 8192, 33000

so when you load it back with LOAD CODE, it will be automatically launched
with an implicit RANDOMIZE USR 33000.

Each file can be referred both through its name and its directory number, so
if file "screen" is listed as number 7 you may also enter:
 
 LOAD p7

Note that if you use the abbreviated notation, each file will be loaded
accordingly to its type (i.e. you can a CODE file will be loaded into memory
at its start address).

Of course MERGE and VERIFY are also available with a similar syntax.

To erase a file from the disk, enter:

 ERASE d1;"file2del"
 ERASE d1;"*"                dangerous!

The ERASE command can also be used to rename a file:

 ERASE d1;"oldname" TO "newname"

To format a disk, use:

 FORMAT d1                   double density (250 Kbit/sec)

or

 FORMAT sd1                  single density

GDOS also extends streams, so that you can redirect a stream to a file and
vice versa. If you open a channel for writing to a disk file, then an OPENTYPE 
file is created. Opentypes can be more than 64K in length. 
Channels are accessed with the usual PRINT, INPUT, INKEY$, etc. commands. 
Examples:

 OPEN #4;d1;"archive"
 OPEN #5;d1;"temp" OUT       open for writing only
 OPEN #5;d1;"temp" IN        open for reading
 MOVE #3 TO #4
 MOVE #4 TO d1;"temp1"
 MOVE d1;"temp2" TO #4
 CLOSE #4

Note that disk-mapped channels are buffered, so data is read/written to
disk only when the 512 bytes buffer is empty/full.
When accessing BASIC, CODE, DATA and SCREEN$ files through streams, remember
that these files start with a 9 bytes header and the actual data starts at
byte 10.

To copy a file into another, use:

 SAVE d1;"file1" TO d2;"file2"

Since the SAVE TO command uses all the RAM available, when it has finished a
system reset occurs.

You can LOAD/SAVE single disk sectors with this syntax:

 LOAD @d,t,s,address
 SAVE @d,t,s,address

where 'd' is a drive number (1 or 2)
      't' is the track number (0..79 + 128 if side 1)
      's' is the sector number (1..10)
      'address' is the address of the 512 bytes buffer

For example, you may read the first sector of the disk (which holds file 
descriptors number 0 and 1) with LOAD @1,0,1,40000.

DISCiPLE GDOS recognizes the Microdrive syntax, so you can enter commands
like this:

 LOAD *"m";1;"pippo"

which will load the BASIC program pippo from drive 1. All your microdrive
programs should run over GDOS without modifications. Remember that PlusD
does not support the IF1 syntax.





9.1 THE NETWORK
===============

GDOS (DISCiPLE) implements an IF1 compatible network, with some enhancements. 
Up to 63 Spectrums can be connected together and share their resources (files 
and printers) simply through a 3.5 mm mono jack cable.
Each station is given an unique station number ranging from 1 to 63.
The station number is assigned with the command:

 FORMAT Ns

where 's' is the station numer (1-63). This command can be entered even
without having the system file loaded (i.e. system not booted).

Station number 0 is reserved for broadcasting. If you enter FORMAT N0, the
network is switched off; type FORMAT Ns to switch it on again.

Station numbers are divided into four classes:

Number Purpose
----------------------------------------------------------------
    0  Broadcasting
    1  Master station
  2-9  Assistants (they load the system file)
10-63  Pupils or assistants (pupils do not load the system file)

The following network configurations are possible:

1. Shared Access Network
------------------------

In this model, station number 1 owns the resources (disk drives and printer)
and acts as a master. The other stations are called pupils and can
access files which are onto the master's disks and print with the master's
printer. Only the master must load the system file. Since they don't have to
load the system file, pupils are identified with station numbers greater
or equal than 10. So, if you try to enter FORMAT N8 without the system loaded,
you get an 'Invalid station number' error message.

The master can send a file "pippo" to pupil number 16 with:

 LOAD d1;"pippo"           first load the file, a Basic program in this case
 SAVE N16                  send it to station 16

Of course you can send CODE files, SCREEN$, etc. too!
You can send the file to all the stations using broadcast:

 SAVE N0                   send to all

Station 6 can receive the program from the master entering:

 LOAD N1                   receive from station 1 (the master)

Each station can receive a broadcast message with:

 LOAD N0

Pupils can also send broadcast messages with SAVE N0 and communicate with
other pupils in the same way.

The most interesting thing is that a pupil can enter disk and printing
commands as if the disk drives and the printer would be connected to it.
So, station number 6 can get the master's disk directory simply with:

 CAT d1

and load file "pippo" with:

 LOAD d1;"pippo"

Of course pupils can also save files onto the master's disk, and use its
printer with the common

 LLIST, LPRINT or COPY SCREEN$

commands.

The master has the ability to force data transfer from and to a pupil
station. On the master, if you type:

 LOAD F4 SCREEN$

then the Spectrum number 4 will stop and transfer its current SCREEN$ to
the master, which can therefore see what's going on at station 4.
Similarly, you can also enter:

 SAVE F8

which will force station number 8 to load the Basic program currently loaded
onto the master.
Again, any variation of the LOAD/SAVE commands will work (CODE, SCREEN$...).

Of course the master can use the system normally.

2. Independent Station Network
------------------------------

It is very similar to the previous model, but now each station has its own
disk drives and printer. Of course all the stations must load the system
file in this case, and the FORMAT command must be issued after that.

For example, station 4 can send a CODE block to station 3 with:

 SAVE N3 CODE 32768, 16384

and station 3 will receive it with:

 LOAD N4 CODE

You can use station number 0 for broadcasting.
Note that the master station in the previous model is an independent station.
Important note: only stations number 1 - 10 can be independent stations.
Stations 2 - 10 are called assistants (act like masters but cannot enter
SAVE F- and LOAD F- commands).

3. Mixed Network
----------------

It is possible to have a network with both pupil and independent stations -
the pupil stations being those without their own disk drives or printers.
In this way it is possible to have more than a master.





9.2 THE SNAPSHOT BUTTON
=======================

When you press the magic button, an NMI is generated and control passes to
address 0x0066 (102 dec.) of the DISCiPLE/+D memory. The consequent behaviour
of the system depends on the particular System version loaded. Under the
standard systems (eg. systems 3a/3b/3d), you have to hold down CAPS SHIFT
while pressing the button and then colored stripes appear in the border and
five keys are active:

  1 = Dump screen to printer
  2 = Big screen dump (A4)
  3 = Save current screen to disk
  4 = Save a 48K snapshot
  5 = Save a 128K snapshot.

Snapshots are saved to disk with names like "Snap A" and subsequent indexes
depending on their position in the directory. When saving a 128K snap, the
system stops after creating the file and waits for the user to specify if the
screen has changed since the beginning of the operation; the user must respond
pressing either 'y' or 'n'. This happens because unlike Multiface the DISCiPLE
and the +D haven't got any flip flop to store the status of port 0x7FFD bit 3
which tells which videoram is displayed. Before waiting for the user
intervention, the system pages the first videoram (0x4000 page 5), so if the
image displayed changes then it means that the second videoram was previously
paged. Well, that's it!

After that, control is passed back to the interrupted program.

NOTE: The snapshot routine corrupts the stack with six bytes (PC,AF and R+F).
This may cause some programs which use the stack in a particular way to
crash if the magic button is pressed at certain times (eg. Batman the Movie).
See the snapshot section (file type 5) in chapter [7] for more details.

NOTE: The snapshot feature cannot be used while the network is in use.





9.3 GDOS and UNIDOS ERROR MESSAGES
==================================

Here's a list of the error codes for both systems available for the RST 20h
service.

-------------------------------------------------------------
Code |        GDOS                |        G+DOS
-------------------------------------------------------------
 00  |  Nonsense in GDOS          |  Nonsense in G+DOS
 01  |  Nonsense in GNOS          |  Nonsense in GNOS
 02  |  Statement end error       |  Statement END error
 03  |  BREAK requested           |  BREAK requested
 04  |  SECTOR error              |  SECTOR error
 05  |  FORMAT data lost          |  FORMAT data lost
 06  |  NO DISC in drive          |  CHECK DISC in drive
 07  |  No "SYSTEM" file          |  NO "+SYS  " file
 08  |  Invalid FILE NAME         |  Invalid FILE NAME
 09  |  Invalid STATION           |  Invalid STATION
 10  |  Invalid DEVICE            |  Invalid DEVICE
 11  |  VARIABLE not found        |  VARIABLE not found
 12  |  VERIFY failed             |  VERIFY failed
 13  |  Wrong FILE type           |  Wrong FILE type
 14  |  MERGE error               |  MERGE error
 15  |  CODE error                |  CODE error
 16  |  PUPIL set                 |  PUPIL set
 17  |  Invalid CODE              |  Invalid CODE
 18  |  Reading a WRITE file      |  Reading a WRITE file
 19  |  Writing a READ file       |  Writing a READ file
 20  |  O.K. GDOS 3               |  O.K. G+DOS
 21  |  Network OFF               |  Network OFF
 22  |  Wrong DRIVE               |  Wrong DRIVE
 23  |  Disc write PROTECTED      |  Disc write PROTECTED
 24  |  Not enough SPACE on disc  |  Not enough SPACE on disc
 25  |  Directory FULL            |  Directory FULL
 26  |  File NOT FOUND            |  File NOT FOUND
 27  |  END of file               |  END of file
 28  |  File NAME used            |  File NAME used
 29  |  Not a MASTER station      |  NO G+DOS loaded
 30  |  STREAM used               |  STREAM used
 31  |  CHANNEL used              |  CHANNEL used
-------------------------------------------------------------        


----------------------------------
 Code |        UNIDOS
----------------------------------
 128  |  Nonsense in Uni-Dos
 129  |  O.K Uni-Dos
 130  |  Break requested
 131  |  Corrupt sector
 132  |  Sector missing
 133  |  Check disc in drive
 134  |  DOS file not found
 135  |  Invalid filename
 136  |  Invalid sector number
 137  |  Invalid device/channel
 138  |  Wrong stream type
 139  |  Verification failed
 140  |  Wrong file type
 141  |  CODE parameter error
 142  |  Directory not found
 143  |  File has zero length
 144  |  Reading a write file
 145  |  Writing a read file
 146  |  POINT outside file
 147  |  Channel out of order
 148  |  Illegal drive number
 149  |  Disc write protected
 150  |  Not enough disc space
 151  |  Directory full
 152  |  File not found
 153  |  End of file
 154  |  Filename already used
 155  |  File still open
 156  |  File in use
 157  |  Channel already open
 158  |  Protected file
 159  |  Unavailable RST 8





10. GDOS and UNIDOS SYSTEM VARIABLES
====================================

GDOS and UNIDOS system variables are stored into the interface's RAM and can
be modified with the POKE command in the following form:

            POKE @var, value

where:

              var  is a variable number
            value  is the new variable value.

Actually, the '@' operator is interpreted as an offset into the interface's
RAM. The base addresses are the following:

 0x2000 UNIDOS and G+DOS (+D)
 0x0298 GDOS (DISCiPLE)

List of the system variables:

VAR# Description
-----------------------------------------------------------------------------
  0  Flash border during disk operations. Set to 0 to leave the border
     unaltered. This byte is ANDed with the sector number currently accessed
     and then sent to port 0xFE.
  1  Drive 1 capacity = number of tracks + 128 if double sided.
  2  Drive 2 capacity, same as above.
  3  Drive stepping rate. Set to 1 for the minimum (1ms).
     WARNING: Poking 0 here may lock your disk drive. It can be unlocked
     reinstalling the OS from tape.
  4  GDOS: disable Centronics printer port (0=enabled)
     UNIDOS: Enable BREAK key if set.
  5  Printer line length in number of characters (default 80)
  6  Printer control flag. If set the codes sent to the printer are not
     filtered (binary output). Necesssary to send control codes to the
     printer.
  7  Printer line spacing expressed in n/72 of an inch. It is sent to the
     printer before avery CR (default GDOS=12, UNIDOS=8).
  8  Number of line feeds after CR (default: GDOS=1 UNIDOS=0).
  9  Left margin for printing. This is the number of spaces inserted before
     the first character of a line (default=0).
 10  Printer flag.
     GDOS: if set then the printer driver generates the graphic representation
     of '' and ',' (default=1).
     UNIDOS: printer flag (default=0x80).
 11  GDOS: network station number (default=1).
     UNIDOS: Centronics enable, same as GDOS variable #4 (default=1).
 12  UNIDOS: printer column number (default=1).
 13  UNIDOS: CLS# screen color.
 14  Extended syntax address (2 bytes). This address is called on error which
     are not related to hook codes and DOS syntax. Can be used to add extra
     commands. Ignored if 0.
 16  UNIDOS: Interrupt address (2 bytes).
 18  UNIDOS: Printer initialization codes (8 bytes). They are sent to the
     printer after a NEW or before pressing the 'P' key during a snapshot.
 26  UNIDOS: Set character pitch (8 bytes).
 34  UNIDOS: Set n/72 line space (8 bytes).
 42  UNIDOS: Set UDG bit graphics density (8 bytes).
 50  UNIDOS: Second initialise codes (8 bytes).
 58  UNIDOS: Codes for '' (8 bytes).
 66  UNIDOS: Codes for '#' (8 bytes).
 74  UNIDOS: Codes for (C) (8 bytes).
 82  UNIDOS: Save SCREEN$ 2 parameters (7 bytes).
 89  UNIDOS: set dump graphics (8 bytes).
 97  UNIDOS: address of extra error messages (default=0x1C68).
 99  UNIDOS: error code
100  UNIDOS: address of LPRINT routine (default=0x34AA).
102  UNIDOS: DOS error return address (default=0x0000).
104  UNIDOS: snapshot workspace (20 bytes).
124  UNIDOS: called on reset (default=0x0000).
126  UNIDOS: called on boot (default=0x21A4).
7667 UNIDOS: set this to 0 to reset DOS.





11. UNIDOS EXTENDED BASIC SYNTAX
================================

UNIDOS is an advanced operating system which runs both on DISCiPLE and
PlusD and is available as an EPROM upgrade separately for the two interfaces.
To install it, get the EPROM chip specific for your interface and replace the
GDOS ROM with it. Of course you also need the system disk which contains the
RAM resident portion of the DOS, a file called "Uni-Dos" which is launched
with the usual RUN command when the computer is switched on.
The system file is exactly the same both for the DISCiPLE and the +D (hence
the name UNI-DOS, I suppose).
It is 6654 bytes in length; the "missing" two bytes contain a checksum which
is constantly monitored by the DOS to detect system corruptions.
This mechanism works quite well and sometimes you'll see that the system
file is loaded without an explicit statement: just don't worry! :)
Also remember that in the DISCiPLE the RAM and ROM addresses are swapped under
UNIDOS. See chapters [2] and [3.1] for all the details.

The main UNIDOS features are powerful disk management with subdirectories,
excellent printing facilities and a lot more of professional touches that
you discover with use, making it extremely powerful.

UNIDOS provides a superset of the standard GDOS and G+DOS functions (some
of them have been changed, however), so read the related chapter first if you
don't know that already. Some parts are missing, such as the network routines
which have been suppressed for space reasons. Also the FORMAT statement is no
more part of the command set, but it is provided as a separate program in the
system disk.

First of all, files now have two attributes: hidden and protected. Hidden
files are not showed in the catalogue, while protected files are read-only.
Also, the disk is given a name (a string containing up to 10 characters)
during the FORMAT process.

As already said, UNIDOS introduces SUBDIRECTORIES. They work in the same
way as you'd expect, so whenever a filename has to be specified you may
use a complete path:

 "/dir1/dir2/file"

Note that the slash '/' is used to separate the directory names, just like
in Unix. Pathnames can be relative to the current directory or absolute
(i.e. relative to the root, starting with a '/'). There is no limit to
the depth of the directory tree. The root directory has a fixed dimension
of 80 file entries, while subdirectories may have any capacity.
If the string ends with the slash charachter, then it is a directory name.
The special directory names "." and ".." obviously refer to the current
and the parent directory, respectively.

The equivalent of the 'cd' (change directory) command is:

 IN d1;"pathname/"

with the ending slash in the pathname (because it must be a directory name);
this sets the current working directory and the current drive. You may also
use IN to set the current drive only, just omit the pathname and the
semicolon.

There are no standard commands to create and remove directories. See the
CREATE files paragraph later.

The LOAD and SAVE statements are unchanged; an extra abbreviated form has
been introduced for LOAD (and MERGE and VERIFY too, of course):

 LOAD p"filename"

which loads "filename" from the current disk.
EXECUTE files can be launched with:

 LOAD d1;"exe"X, <address>

In the SAVE statement you may specify the OVER keyword to avoid the overwrite
check:

 SAVE OVER d1;"program"

This will overwrite a previous file without asking for confirmation.

The ERASE command is unchanged. If NOT is added after the ERASE
statement, then no error is reported. You cannot remove a file if it is
currently open or it is protected.

The CAT statement has a new form:
 
 CAT d1
 CAT d1;"pathname"

You must now specify the 'd1' instead of just '1' as in GDOS. All the GDOS
variants are accepted.
If you add NOT after CAT, then it will list the hidden files too.
If you specify a directory name, CAT lists the directory contents.

Now it possible to MERGE CODE files too, but the only effect is that the
autostart is removed.

The MOVE statement works as usual (OVER allowed) and it can be now used to
copy one file to another, replacing the old SAVE TO in this way:

 MOVE [OVER] d1;"file1" TO d2;"file2"
 MOVE [OVER] d1;"file1" TO "file2"

MOVE can copy snapshots, MDRV and opentype files too, even longer than 64K.
It can copy entire subdirectories if a directory name (ending with '/') is
specified.
Unlike SAVE TO, MOVE uses only the memory between the BASIC area and the
machine stack, so it does not require a system reset when it has finished.

The CLS command can be used to reset the screen colors to those stored in
the system variable 13:

 CLS #

A great facility UNIDOS introduces are RANDOM ACCESS FILES, i.e. OPENTYPE
files which can be accessed in random way, not only serially one byte
after another.
To open a random file, the OPEN # statement is used in this form:

 OPEN #4;d1;"file" RND

If you specify IN instead of RND, the file is read only but still has random
access. Up to 16 channels can be attached to the same file at once.
This statement:

 OPEN #4;d1;"file" RND <length>[,<byte>]

creates the file of the specified length and fills it with the specified
byte (if specified!).
Remember to close or clear all channels before you remove the disk from
the drive, or else an error will be given when you enter DOS commands after
the disk swapping.

You can work with channels using the usual PRINT, INPUT and INKEY$ commands
with all the respective variants. However, some new commands are available:

 POINT #4, <offset>

will set the file pointer at the specified offset of the random access
channel #4. An error is given if the file boundaries are crossed.

The CLEAR statement has now two forms:

 CLEAR #
 CLEAR #*[<channel>]

The former clears all channels without creating an openout file, the latter
closes one or all the disk channels creating an openout file and flushing
the buffers.
You may flush the buffers only, without closing the file, with:

 OUT #<channel>

As we said above, a special care has been involved in the PRINTING section of
UNIDOS. The LPRINT and LLIST commands work in the usual way, now redirected
to the parallel port of the interface.
You can print a screen dump with:

 SAVE SCREEN$ 1   or   SAVE SCREEN$ 2

each using a different preset of parameters. The second preset can be user
defined, just alter the relative system variables. These are also the
routines invoked by the snapshot keys '1' and '2' (see later).
The most general and powerful form of SAVE SCREEN$ is the following:

 SAVE SCREEN$ #flag [,pass [,margin [,y [,x [,h [,w]]]]]]

where flag = horiz. magnification (0-7) + 8 * vert. magnification (0-7) +
           + 64 if you want color processing + 128 if you want sideways
             printing.
             A magnification of 0 actually means 8.
           
      pass = number of passes for a single printing line

    margin = left margin in characthers

     y & x = top left corner of the window to print
     w & h = width and heigth of the window to print

See the system variable list for more advanced settings which affect printing.

An useful statement implements the ON ERROR GOTO mechanism:

  LINE 9000

enables error trapping; all errors but OK, STOP and BREAK are catched and
control is passed to the specified line, where the program can identify the
error type reading system variable 99 with (PEEK @99).

UNIDOS also implements new BASIC FUNCTIONS; they are all surrounded by
brackets, i.e. are in the form of (<function>).
We have just seen the:

 (PEEK @offset)

which reads a system variable (and in general the RAM location offset+8192).
The length of a random channel is obtained with:

 (LEN #<channel>)

while:

 (POINT #<channel>)

returns the current file pointer (offset) or 0 if we are at the end of the
file (EOF).
A specified number of bytes can be read from any channel with:

 (IN #<channel>, <length>)

Lastly, you can check if a file or directory exists with:

 AT d1;"pathname"

which returns 0 if the file does not exist or its directory number if found.

Now let's examine the last new file type introduced, CREATE files.
These are machine code programs (generally new commands or syntax extensions)
that are loaded between the channel area and the BASIC area, so they are
lost after a NEW or a reset.
You may LOAD and SAVE CREATE files with:

 LOAD d1;"pathname" USR
 SAVE d1;"pathname" USR <address>, <length>

You can load as many create files as you need (but the memory space is
obviously affected).
The system disk provided with UNIDOS contains two create files with the
following extensions:

 "ext_code" contains:
            FORMAT d1;"diskname"
              to format disks. The disk name is stored in the last bytes of
              the first root directory entry.
            (LINE)
              returns the current drive number + 128 if the disk is write
              protected and the value is negated if there is no disk in drive.
            (STR$ #<channel>)
              return a null string if the channel is not open, 'd' if it is an
              openout stream and 'D' if it is a random stream, or the letter
              that the channel uses.
 "dir_code" contains:
            SAVE [OVER] d1;"dirname" CAT <capacity>
              creates a directory with a capacity of the specified number of
              files.
            ERASE d1;"dirname" CAT
              removes the whole specified directory.
            (STEP [d<drive])
              returns the pathname of the last directory accessed or of the
              current directory (if the drive number is specified).

Now a few words about the SNAPSHOT. The active keys are the same as in GDOS
with the same meanings, plus the key 'x' to return to the interrupted
program and 'p' which sends the initialization codes to the printer.
If some error occurs during the snapshot saving, then control is passed back
to the snapshot menu and not to the interrupted program.

Note that on the +D the snapshot button is disabled during the processing
of a DOS command.





12. CONNECTORS PINOUTS
======================

The following pinouts are viewed from the back of the interface.

            DISC CONNECTOR
  ------------------------------------   1-33 Ground (0V)   22 Write data
 | 33                             3 1 |     8 Index         24 Write gate 
 |  o o o o o o o o o o o o o o o o o |    10 Disk1 select  26 Track00
 |                                    |    12 Disk2 select  28 Write protect
 |  o o o o o o o o o o o o o o o o o |    16 Motor on      30 Read data
 | 34                             4 2 |    18 Step dir.     32 Side select
  ------------------------------------     20 Step pulse


        PRINTER CONNECTOR
   ----------------------------      1 Strobe        13 D5
  | 25                     3 1 |     3 D0            15 D6
  |  o o o o o o o o o o o o o |     5 D1            17 D7
  |                            |     7 D2            21 Busy (input)
  |  o o o o o o o o o o o o o |     9 D3          2-22 Grounds (0V)
  | 26                     4 2 |    11 D4
   ----------------------------

The parallel pinout allows direct connection to a Centronics connector
simply through a flat cable.





12.1 CONNECTING A PC 5.25" DRIVE
================================

Petri Andras sent an interesting document to explain how to connect a common
5.25" (1.2 MB) PC disk drive to the DISCiPLE and +D. Although not all drives
are suitable for the purpose, the chances to succeed are quite good; you can
decide whether your drive will work or not with a simple test described
below.
Note that the procedure requires a certain experience, so you'd better
ask an expert friend if you are not familiar with such operations. Take care,
we are not responsible for any damage caused to your system.

SUITABILITY TEST. The floppy drive must be able to operate in "low density" mode. 
This is the crucial point, as the DISCiPLE expects a specific RPM from the floppy
drive; the PC floppy controller, however, handles different densities
without changing the floppy drive's RPM, by re-programming its internal
clock frequency. Therefore many PC floppy units, especially later ones, do
not support RPM changing at all. There is a line of the interface for
switching the floppy's RPM (Pin 2), but the floppy unit may ignore it.

This is the operative test: apply power to the floppy with the flat cable 
removed, insert a disk into it, move the jumper to DS0 as described above,
short-circuit pins 11-12 and 15-16 (with two small alligator clamps on the
edge connector). Now the floppy LED will light on and you can hear the
drive motor running. Take a third alligator clamp or a piece of wire, and
short pins 1 and 2. If the RPM of the disk changes (the difference is
audible), then the floppy unit is OK. 
If no change occurs, remove power, get a multimeter and search for a
jumper that is connected to pin 2 of the floppy's edge connector. If you
are lucky, you will find one; try to set it into a different position and
test again.

THE PROCEDURE. The floppy drive must be connected to the edge connector on the
PC floppy cable that is BEFORE the twist (where drive B: is connected in a
real PC). If the floppy cable has an old-style 5.25" edge connector only
after the twist (newer PC floppy cables), the edge connector must be
disassembled, the twisted wires of the flat cable must be straightened,
and the connector must be re-assembled to the cable. This operation
requires a little dexterity, but a real Speccy hacker surely has it ;-)

The floppy drive has a set of four jumpers somewhere, described as DS0,
DS1, DS2, DS3 (or something similar, numbered from 0 to 3). The jumper is
ALWAYS in the DS1 position in the case of PC floppies. This must be moved
to DS0 if you want to use it as Disk 1 on the DISCiPLE. (Disk 2 must have
this jumper on DS1).
Technical note: This jumper actually determines the Drive Select line
that activates the floppy unit. The original Tandon/Shugart floppy
interface supported four Drive Select lines and a common Motor Enable
line. The PC floppy interface uses DS1 and MotorEnable for disk selection
and motor enable for drive A:, and DS0 and DS2 for drive B:. The twist in
the floppy cable ensures that the two floppy units can be jumpered
identically.





13. VL1772 PROGRAMMING INFO
===========================

Here is the low-level technical information about the VL1772 floppy
disk controller. Some devices equipped with this component are MGT DISCiPLE,
MGT PLUS D, MGT SAM COUPE and ATARI ST. It seems to be almost compatible with
other FDC devices such as 1791 and 1793.
See section 3 for the port addresses of the FDC registers in the DISCiPLE
and the +D.

----------------------
-COMMAND REGISTER (W)-
----------------------

Commands are divided into four classes. The lower 4 bits of the command byte
have a different meaning depending on the command class; remember to OR them
with the command codes given below.

Type 1 commands:
----------------

  b0-b1 = Stepping rate
          00 =  6 ms
          01 = 12 ms
          10 = 20 ms
          11 = 30 ms
     b2 = Verify track
     b3 = Load/unload head at beginning

Command name    Code  Comments
----------------------------------------------------------------------------
RESTORE         0x00  Restore disk head to track 0
SEEK            0x10  Seek a track (send the track number to the DATA reg.)
STEP_NUPD       0x20  Step using current dir without updating track register
STEP_UPD        0x30  Step drive using current direction
STEP_IN_NUPD    0x40  Increase track without updating track register
STEP_IN_UPD     0x50  Increase track
STEP_OUT_NUPD   0x60  Decrease track without updating track register
STEP_OUT_UPD    0x70  Decrease track

Type 2 commands:
----------------

     b0 = f8 (deleted dam) / fb (dam) if set in READ commands
     b1 = Enable side compare
     b2 = 15 ms delay
     b3 = Compare for side 1/0

Command name    Code  Comments
----------------------------------------------------------------------------
READ_1SECTOR    0x80  Read one sector
READ_MSECTOR    0x90  Read multiple sectors
WRITE_1SECTOR   0xA0  Write one sector
WRITE_MSECTOR   0xB0  Write multiple sectors

Type 3 commands:
----------------

  b0-b1 = 0
     b2 = 15 ms delay
     b3 = 0

Command name    Code  Notes
----------------------------------------------------------------------------
READ_ADDRESS    0xC0  Read address
                      The controller reads the header of the first sector
                      encountered and produces 6 bytes which must be read:
                      track number, side number, sector number, sector size
                      and a two-byte checksum.
READ_TRACK      0xE0  Read a whole track (including headers and control data)
WRITE_TRACK     0xF0  Write a whole track (used to format the track)

Type 4 commands:
----------------

     b0 = Not ready to read transition
     b1 = Ready to not read transition
     b2 = Index pulse
     b3 = Immediate interrupt, requires reset
  b0-b3 = 0000 -> Terminate with no interrupt

Command name    Code  Notes
----------------------------------------------------------------------------
FORCE_INTERPT   0xD0  Force interrupt (stops the current command)



---------------------
-STATUS REGISTER (R)-
---------------------

Some bits assume a different meaning depending on the last command issued.

After a Type 1 command:

Bit   Meaning             Comments
----------------------------------------------------------------------------
 0    BUSY                Wait BUSY=0 for a new command
 1    INDEX PULSE         Index pulse
 2    TRACK00             Signals head on track 00
 3    CRC ERROR           Sector corrupted
 4    SEEK ERROR          Seek error
 5    HEAD LOADED         Head loaded
 6    WRITE PROTECT       Disk is write protected
 7    MOTOR ON            Motor is on or drive not ready

After a Type 2/3 command:

Bit   Meaning             Comments
----------------------------------------------------------------------------
 0    BUSY                Wait BUSY=0 for a new command
 1    DRQ                 Need to send or read data from DATA register
 2    LOST DATA           Error (eg you did not respect I/O timings)
 3    CRC ERROR           Sector corrupted
 4    RECORD NOT FOUND    Non-existent track/sector or no more data to read
 5    REC.TYP/WR.FAULT    Read: record type; Write: write fault
 6    WRITE PROTECT       Disk is write protected
 7    MOTOR ON            Motor is on or drive not ready



---------------------
-TRACK REGISTER (RW)-
---------------------

Contains the current track number.

----------------------
-SECTOR REGISTER (RW)-
----------------------

Current sector number for read/write operations.

--------------------
-DATA REGISTER (RW)-
--------------------

Here you may read and write the data to the controller. Check the status
register before reading or writing data.





14. CREDITS AND CONTACT INFO
============================

This document was written by Luca Bisti of Ramsoft. 
Stefano Donati wrote chapters 3.1, 5.1, 9.3 and helped with errors correction.

Thanks to Dominic Morris who provided info about hook codes 43h, 44h, 45h
and 47h.
Petri Andras sent the document reported in chapter 12.1.

You may contact these people at the following addresses:

* THE RAMSOFT STAFF:
  Ramsoft WHQ (WWR)... ramsoft@retroplay.com
  Luca Bisti ......... luca.bisti@studenti.ing.unipi.it
  Stefano Donati ..... the.king@flashnet.it

* Dominic Morris ..... djm@jb.man.ac.uk
* Petri Andras ....... petri@mit.bme.hu

You can always get the latest version of this tech at the RAMSOFT homepage:

 http://www.retroplay.com/Mecenate/ramsoft  (World Wide Ramsoft)
 -----------------------------------------  --------------------

 If the address above doesn't work, try:
 http://www.geocities.com/SiliconValley/Bay/5673
 which will redirect you the the current URL for World Wide Ramsoft.

See you there!
