; Commodore 1541 / OC-118 Disk Drive Memory Map
; V1.3 18 Jan 1995
; Covered in this file:
; 1541 / OC-118 Disk Drive RAM Map
; 1541 / OC-118 Disk Drive I/O Area
;
The following text was grabbed from "The anatomy of the 1541" by
Lothar Englisch and Norbert Szczepanowski.
Additions from "1541 levyasema".
Layout of the 2Kb RAM area
==========================
; Commodore 1541 Disk Drive RAM Map
;
; The number in brackets after description is the default value after
; power-up.
; Work queue
0000 Command code for buffer 0
0001 Command code for buffer 1
0002 Command code for buffer 2
0003 Command code for buffer 3
0004 Command code for buffer 4
0005 Command code for buffer 5 (unused)
; ***
0006 - 07 Track and sector for buffer 0
0008 - 09 Track and sector for buffer 1
000a - 0b Track and sector for buffer 2
000c - 0d Track and sector for buffer 3
000e - 0f Track and sector for buffer 4
0010 - 11 Track and sector for buffer 5 (unused)
0012 - 13 Disk ID, drive 0
0014 - 15 Disk ID, drive 1
0016 Header block: ID
0018 Header block: Track
0019 Header block: Sector
001a Header block: Parity
001b Not used (Disk Controller work)
001c Flag for disk change, drive 0 [01]
001d Flag for disk change, drive 1 [01]
001e Flag for write protect sense, drive 0 [01]
001f Flag for write protect sense, drive 1
0020 Drive 0 status (disk and step motor)
; bit 7: Disk drive ready (1 = No, 0 = Yes)
; bit 6: Read/Write head moving (1 = Yes, 0= No)
; bit 5: Motor on (1 = Yes, 0 = No)
; bit 4: Switch off motor (1 = Yes, 0 = No)
0021 Drive 1 status (disk and step motor)
0022 Current track for drive 0
0023 Flag for 1541 (0), 1540 (not 0)
; Not used (track for drive 1)
0024 Scratch pad of GCR conversion
; Storage for BIN -> GCR conversions
002e Pointer for temporary storage WORD
0030 Buffer pointer for disk controller WORD
; Pointer: Active buffer
0032 Pointer: *** active track
0033 Pointer: *** active sector
0034 Pointer to last converted byte
0035 Not used (decode error, GCR)
0036 Byte counter for GCR/BIN conversion
0037 Not used (bit counter)
0038 Constant 7, ID mark for start of data block
0039 Constant 8, ID mark for start of block header
003a Parity for data buffer
003b Not directly used
003c Not directly used
003d Motor flag
; Disk drive number, on 1541 always 00
003e Active drive (FF, if not active)
003f Buffer number for disk controller
; Previous work place in queue (0 - 5)
0040 Byte counter for GCR conversion
0041 Number of next work in queue (0 - 5)
0042 Destination track (to move R/W head to) DATA
0043 Number of sectors per track for formatting DATA
0044 Temp. work area; Scratch pad DATA
0045 Work code temp. storage
0046 Not used
0047 Data block ID char, default 07.
; By changing this value, a data block can be written
; with different ID. The value must be less than 10.
0048 Counter for head movement
; Timer: R/W head acceleration
0049 Stack pointer temp. storage [39]
004a Step counter for head transport
; Values 0 - 127 move the head outside and values over
; 128 move towards the centre.
004b ? (Temp. storage) DATA
004c Last read sector DATA
004d Next sector DATA
004e - 4f Pointer to buffer for GCR->BIN conversion WORD
0050 Flag for GCR format (0=BIN, 1=GCR) DATA
0051 Current track number for formatting [FF] DATA
0052 - 55 Storage for 4 BIN bytes for GCR coding DATA
0056 - 5d Storage for 5 GCR bytes DATA
005e Number of steps for head motor accelerating/decl. [04]
005f accelerating/decl. factor [04]
0062 - 63 Pointer to routine for head movement [FA05] WORD
0064 Minimum number of steps [C8]
0065 - 66 UI vector [$EB22] WORD
0067 Flag: NMI
0068 Flag for disk initialisation DATA
; Automatic disk initialisation if ID MISMATCH occurred (1 = no, 0 = yes)
0069 Step size for sector division [0A]
; Sector number interleave for SEQ files, default 10 (0A)
006a Number of read attempts [5] DATA
006b - 6c Pointer: Start of Jump table for U commands [FFEA] WORD
006d - 6e Pointer: Start of bitmap [0400]
006f - 70 Pointer to address for M & B commands WORD
0071 Temp. work area
0072 Temp. work area [FF]
0073 Temp. work area
0074 Temp. work area
0075 - 76 Indirect pointer [0100]
0077 Listener address (Device number + $20) [28]
0078 Talker address (Device number + $40) [48]
0079 Flag: Active listener
007a Flag: Active talker
007b ?
007c Flag for ATN from serial bus receiving
; ATN interrupt
007d Flag for ATN on serial bus active
007e Last handled program
007f Drive number (on 1541 always 00)
0080 Current Track number
0081 Current Sector number
0082 Channel number (Logical index)
0083 Secondary address
0084 Original Secondary address [6F]
0085 Current Data byte [3F]
0086 - 8a Temp Results
008b - 8e Work storage for division
; Result, Multiply and divide
008f - 93 ?
0094 - 95 Current buffer pointer WORD
; Pointer: Directory buffer (0204)
0096 ?
0099 - 9a Pointer: Next byte in buffer 0 [0300]
009b - 9c Pointer: Next byte in buffer 1 [0400]
009d - 9e Pointer: Next byte in buffer 2 [0500]
009f - a0 Pointer: Next byte in buffer 3 [0600]
00a1 - a2 Pointer: Next byte in buffer 4 [0700]
00a3 - a4 Pointer: Next byte in command buffer [0200]
00a5 - a6 Pointer: Next byte in error message buffer [02D6]
00a7 - ad Table: Non-active channel numbers for each buffer
00ae - b4 Table:
00b5 - ba Table: Record # low , block # low
00bb - c0 Table: Record # high, block # high
00c1 - c6 Write pointer for REL file
; Table: next record numbers
00c7 - cc Table: Record length for REL file
00cd - d2 Table: Side sectors
00d3 ?
00d4 Pointer in record for REL file
00d5 Side sector number
00d6 Pointer to data block in side sector
00d7 Pointer to record in REL file
00d8 - dc Directory sectors
00dd - e1 Index: Directory
00e2 - e6 Default disk drive [00]
00e7 - eb File type (wild cards, @, closed)
00ec - f1 File type (channel)
00f2 - f7 Channel status
00f8 Flag for EOI
00f9 Current work (Buffer number)
00fa - fe Last used table
00ff Flag: FF = drive 0 not ready (No disk), 00 = ready
0100 Flag: FF = drive 1 not ready (No disk), 00 = ready
0101 Format marker, drive 0
; DOS version (from track 18 sector 0)
0102 Format marker, drive 1
0103 Not used
0104 - ff Stack area
0146 ?
01ba Buffer for GCR code
0200 - 29 Buffer for command string
022a Command code
;022b - 2d Array: Logical index (LINDX)
; Array of status bytes for each channel (secondary address)
; Possible values:
; FF = inactive
; 81 = opened for writing
; 41 = read/write
; 01 = opened for reading
022b Logical index, channel 0
022c Logical index, channel 1
022d Logical index, channel 2
022e - 43 Last read/written byte for each channel
0244 - 49 Pointer: Last char on channel.
; Points to the last character read/written in buffer.
024a Type of active file
024b String length
024c Temp. channel number (secondary address)
024d Current work with drive number
024e Work area to find the best sector
024f - 50 Buffer allocated
0251 Flag: BAM changed, drive 0
0252 Flag: BAM changed, drive 1
0253 Flag for directory entry found (FF = Not found, 00 = Found) DATA
0254 Flag for directory output
0255 Flag: Waiting for command
0256 ?
0257 Last used buffer
0258 Record length
0259 Track of side sector
025a Sector of side sector
025b - 5f Last work (buffers)
0260 - 65 Directory sector (buffers)
0266 - 6b File's index in directory (buffers)
026c Counter for LED flash
; Error Message
026d Error LED
026e Drive for last program
026f sector for last program
0270 Write LINDX
0271 Read LINDX
0272 - 73 Number of blocks (temp)
0274 Length of input line
0275 Char to interpret
0276 Index: End of filename in command buffer
0277 ?
0278 Number of file names
0279 ?
027a - 7f Pointer table: Filenames
0280 - 84 Track of a file
0285 - 89 Sector of a file
028a Flag: wild cards
028c Number of drive(s ?) to look for
028d Flag: Looking for drive
028e drive with last write/open error, used as default drive
028f Flag: Found in directory
0290 Directory sector
0291 Sector for first available file
0292 Index (in directory) for first available file
0293 For the last directory entry 0
0294 Current buffer-index
0295 Counter: Files
0296 Flag: Name matching wild cards
0297 Active operating mode (R or W)
0298 Flag: Work return
0299 Pointer: Re-read error
029a Total tracks
029b - 9c Pointer: BAM last update
029d - a0 BAM: image sector (drives 0 and 1)
02a1 - b0 BAM image
02b1 - d4 Buffer for directory output
02d5 - f8 Buffer for error message
02f9 Flag: Don't write BAM
; This flag is reset to zero before and after each command
02fa - fb Number of free blocks, low byte for drives 0 ja 1
02fc - fd Number of free blocks, hi byte for drives 0 ja 1
02fe - ff Stepper motor sequence
0300 Buffer 0
0400 Buffer 1
0500 Buffer 2
0600 Buffer 3
0621 - 22 Formatting counter
0700 Buffer 4
07ff End of RAM
Layout of the I/O Ports (VIA 6522)
==================================
VIA 1: 6522, port for serial bus
-------------------------------
$1800 PB, port B
$1801 PA, port A
$1802 CB, data direction port B
$1803 CA, data direction port A
$1805 Timer
PB 7, CB2: ATN IN
PB 6,5: Device address preset switches
PB 4: ATN acknowledge OUT
PB 3: CLOCK OUT
PB 2: CLOCK IN
PB 1: DATA OUT
PB 0: DATA IN
VIA 2: 6522, port for motor and read/write head control
------------------------------------------------------
$1C00 PB, control port B
$1C01 PA, port A (data to and from read/write head)
$1C02 CB, data direction port B
$1C03 CA, data direction port A
PB 7: SYNC IN
PB 6,5: Bit rate D1 and D0
PB 4: WPS - Write Protect Sense (1 = On)
PB 3: ACT - LED on drive
PB 2: MTR - drive motor
PB 0,1: step motor for head movement
CA 1: Byte ready
CA 2: SOE - Set Overflow Enable for 6502
CA 3: read/write
Disk Controller Routines
========================
This table contains the addresses and the assigned buffers:
JOB TRACK SECTOR BUFFER
00 06 07 0300-03FF
01 08 09 0400-04FF
02 0A 0B 0500-05FF
03 0C 0D 0600-06FF
04 0E 0F 0700-07FF
05 10 11 -no ram-
If a disk controller routine is to be performed in the interrupt, one
writes the job code and the track and sector numbers of the block to be
processed (if necessary) in the appropriate memory locations. Now the
job code can be passed. This job code has a value greater than 127 (the
7th bit is set). In order to wait until the job is finished, only the
seventh bit need be tested. If this bit is cleared, the job is completed.
The disk controller can perform the following jobs:
JOB NAME DESCRIPTION
80 READ Read sector
90 WRITE Write sector
A0 VERIFY Verify sector
B0 SEEK Find sector
C0 BUMP Bump, Find track 1
D0 JUMP Execute program in buffer
E0 EXECUTE Execute program, first switch drive on and find track
The verify job (A0) is performed automatically after writing a blcok.
If the job ends in an error then the memory location with job command
code is replaced with and error code. Here is a list of the error numbers:
CODE MEANING DOS ERROR MESSAGE
01 Everything OK 00, OK
02 Header block not found 20, READ ERROR
03 SYNC not found 21, READ ERROR
04 Data block not found 22, READ ERROR
05 Checksum error in data block 23, READ ERROR
07 Verify error 25, WRITE ERROR
08 Disk write protected 26, WRITE PROTECT ON
09 Checksum error in header block 27, READ ERROR
0B Id mismatch 29, DISK ID MISMATCH
0F Disk not inserted 74, DRIVE NOT READY
Error codes 06 and 0A do not occur on the 1541.
(
geocities.com/timessquare/arcade/Arcade/2045/docs) (
geocities.com/timessquare/arcade/Arcade/2045) (
geocities.com/timessquare/arcade/Arcade) (
geocities.com/timessquare/arcade) (
geocities.com/timessquare)