Programming the 1770 disc controller
WD1770/2/3 data (disk controller chip)
======================================
This file contains essential data on programming the floppy disk controller
chip used in BBC B+, Master, BBC B with Opus DDOS and some Archimedes
computers. Please note that a lot of the information in the relevent data
sheet has had to be cut out.
Register summary
================
Address offset Contains on read on write
------------------------------------------------------
0 Status Command
1 ------- Track --------
2 ------- Sector -------
3 ------- Data ---------
Command summary
===============
Command register bits
Type Command 7 6 5 4 3 2 1 0
-------------------------------------------------------
I Restore 0 0 0 0 h v r1 r0
I Seek 0 0 0 1 h v r1 r0
I Step 0 0 1 u h v r1 r0
I Step in 0 1 0 u h v r1 r0
I Step out 0 1 1 u h v r1 r0
II Read sector 1 0 0 m h/s e 0/c 0
II Write sector 1 0 1 m h/s e p/c a
III Read address 1 1 0 0 h/0 e 0 0
III Read track 1 1 1 0 h/0 e 0 0
III Write track 1 1 1 1 h/0 e p/0 0
IV Force interrupt 1 1 0 1 i3 i2 i1 i0
Where :
h = motor spin-up sequence disable flag. (1770/2 only)
= 0 Enable spin-up sequence if motor is currently not running.
= 1 Disable spin-up sequence.
v = verify on destination flag. (all)
= 0 Do not verify
= 1 Verify (adds a 30 msec head settling time onto command execution)
r1,r0 = head track-to-track stepping rates. (all)
r1 r0 1770/3 1772
0 0 6 ms 6 ms
0 1 12 ms 12 ms
1 0 20 ms 2 ms
1 1 30 ms 3 ms
u = update track register. (all)
= 0 Do not update track register
= 1 Update track register.
m = multiple sector read/write flag. (all)
= 0 read/write 1 sector only.
= 1 read/write sectors on current track until command is interrupted
using the FORCE INTERRUPT command.
s = side compare flag (1773 only)
= 0 Compare for side 0.
= 1 Compare for side 1.
a0= data address mark type. (all)
= 0 Write normal data mark.
= 1 Write deleted data mark.
e = Head settling delay. (all)
= 0 No delay
= 1 Add 30 ms delay (15 ms on 1772)
c = Side compare flag. (1773 only)
= 0 Disable side compare.
= 1 Enable side compare.
For all type III commands bit 1 must be 0
p = Write precompensation flag. (all)
= 0 Enable write precompensation.
= 1 Disable write precompensation.
i3= 1, immediate interrupt. (all)
i2= 1, interrupt on every index pulse. (all)
i1= 1, Ready to not ready transition. (1773 only)
i0= 1, Not ready to ready transition. (1773 only)
Data formats:
=============
Read address.
Byte Contains
---------------------------
0 Track number
1 Side number
2 Sector number
3 Sector length
4 CRC check byte (1)
5 CRC check byte (2)
Write track (format a track)
Double density formats:
=======================
Recommended | Acorn ADFS |
format | (master 128) |
No. of Hex value | No. of Hex value |
bytes to write | bytes to write | Info
-----------------------+----------------------+-------------------------------
60 4E | 60 4E | Post-index Gap (Gaps 1+2)
/ 12 00 | / 12 00 | Pll lock-up time
| 3 F5 | | 3 F5 | 3 synchronisation bytes
| 1 FE | | 1 FE | ID address mark
| 1 | | 1 | Track number
| 1 | | 1 | Side number
| 1 | | 1 | Sector number
| 1 | | 1 01 | Sector length
| 1 F7 | | 1 F7 | Writes 2 CRC bytes
| 22 4E | | 22 4E | Sector ID / Data Gap (Gap 3a)
| 12 00 | | 12 00 | /Write splice time (Gap 3b)
| | | | \Pll lock-up time
| 3 F5 | | 3 F5 | 3 synchronisation bytes
| 1 FB | | 1 FB | Data address mark
| n | | 256 (5A on format)| Data (number of bytes depends
| | | | on the sector length)
| 1 F7 | | 1 F7 | Writes 2 CRC bytes
\ 24 4E | \ 43 4E | Post Data Gap (Gap 4)
668 approx 4E | 4E | Runout Gap. Write until
| | next index hole.
Single density formats:
=======================
Recommended | Acorn 1770 DFS 2.24 |
format | (master 128) |
No. of Hex value | No. of Hex value |
bytes to write | bytes to write | Info
----------------------+----------------------+--------------------------------
40 FF | 40 FF | Post index Gap (Gaps 1+2)
/ 6 00 | / 6 00 | Pll lock-up
| | | 3 F5 | 3 synchronisation bytes
| 1 FE | | 1 FE | ID address mark
| 1 | | 1 | Track number
| 1 | | 1 | Side number
| 1 | | 1 | Sector number
| 1 | | 1 01 | Sector length
| 1 F7 | | 1 F7 | Writes 2 CRC bytes
| 11 FF | | 10 4E | Sector ID / Data Gap (Gap 3a)
| 6 00 | | 4 00 | Pll lock-up (Gap 3b)
| | | 3 F5 | 3 synchronisation bytes
| 1 FB | | 1 FB/F8 | Data address mark
| n | | 256 (5A on format)| Data
| 1 F7 | | 1 F7 | Writes 2 CRC bytes
\ 10 FF | \ 10 FF | Post data Gap (Gap 4)
369 approx FF | FF | Runout Gap. Write until
| | next index hole.
Write the bracketed area the following times:
Sector length Sector size (n) Number of times to write
-------------------------------------------------------------
00 128 ?
01 256 16 (ADFS 16, DFS 10)
02 512 ?
03 1024 5
Notes
1) The gaps can be altered to a minimum of:
Single density Double density
Gap 1 16 32
Gap 2 11 22
Gap 3a 10 24
Gap 3b 4 8
Gap 4 10 16
2) The reliability depends on the gaps. For highest reliability,
use the recomended formats.
3) The 177X will not automatically detect which density it is use.
There is usually a separate register or a hard link to set up the
denstiy. This applies to all commands.
Status register.
================
The meaning of the bits in the status register depends on which type of
command is currently executing.
Bit | Type I | Type II | Type III | Comments
----+------------------+---------------+---------------+-------------------
7 | Motor on | ---------- Motor on --------- | / If bit 3 is
6 | Not used. | -- Disk is write protected. - | | set then:
5 | Motor spin-up | Data type : 0 = normal. | | If bit 4 is
| completed. | 1 = deleted. | | set, the error
4 | Record not found | ----- Record not found ------ | / is in the ID
3 | CRC error. | --------- CRC error --------- |< field. If bit 4
2 | Not track 0 | ------ Lost data / byte ----- | \ is clear, the
1 | Data Request | -------- Data request ------- | | error is in
0 | Busy | ------------ Busy ----------- | \ the data field.
Note that after a reset, some 177X's say that they are busy, when they are
idle. This happens when you reset the chip while a command is in progress.
Read/Write delay times
======================
There are certain delay times that must be taken into account:
Operation Next operation Delay required
Single Double density
----------------------------------------------------------------
Write command / Read busy bit 48 usec 24 usec
register \ Read status bits 1-7 64 usec 32 usec
Write any reg Read same register 32 usec 16 usec
Drive control register
======================
This controls various functions that the 177X is unable to:
Master drive control:
Bit Meaning
-----------------
7,6 Not used.
5 Double density select (0 = double, 1 = single).
4 Side select (0 = side 0, 1 = side 1).
3 Drive select 2.
2 Reset drive controller chip.
1 Drive select 1.
0 Drive select 0.
B+ drive control:
Bit Meaning
-----------------
7,6 Not used.
5 Reset drive controller chip.
4 Interrupt ?
3 Double density select (0 = double, 1 = single).
2 Side select (0 = side 0, 1 = side 1).
1 Drive select 1.
0 Drive select 0.
Opus double density board on BBC:
Bit Meaning
-----------------
7 Not used.
6 Density select (0 = single, 1 = double).
5-2 Not used.
1 Side select (0 = side 0, 1 = side 1).
0 Drive select (0 = drive 0, 1 = drive 1).
Note that only 1 drive select bit line should be set at a time.
Addresses of registers:
=======================
Computer Location of disk chip & chip Location of drive control
---------------------------------------------------------------------
BBC B with Opus &FE80 - &FE83 WD1770 &FE84
BBC B+ &FE84 - &FE87 WD1770 &FE80
BBC Master &FE28 - &FE2B WD1770 &FE24
Archimedes ? WD1772 ?
I am aware that some archimedes used the WD1772 is used, but if anyone
knows the addresses, I will be happy to put them in.
poppy@poppyfields.net