Posted By
MMS
on 2015-09-19
16:58:58
 |  Re: 1551 question
Well, two questions:
1) I just run into a proper description of the 1551 on the Zimmers. (pls see below)
How I can add it to the HW description of the 1551?
2) It is mentioned in the Plus/4 world 1551 section, that it is easy to detect, which drive connected to the Plussy, 1551 or 1541.
a) If easy, could someone give a description? Even via BASIC PEEKs it is possible? 
b) could we add it to the 1551 descripiton, and then it will be easy to find next time too
1551 description (BTW Attila Grosz also helped it in some way):
QUOTE
This information applies to Commodore 1551 Disk Drive used with plus/4.
Diskettes created on the 1551 are read write compatible with Commodore
1540/1541, 4040, 2031 disk drives. The 1551 is connected to the
computer through the "TCBM" interface. This interface is specially
created by Commodore. Bytes are transferred as parallel data with a
8-bit bi-directional port, two handshake lines, and two status lines.
This handshake protocol allows for less timing constraint than slower
serial interfaces. Estimated data rate over the TCBM handshake is
1600 bytes per second versus 300-400 bytes per second for the 1541
drive. The 1551 connector plugs into the host computer's expansion
port and allows external cartridges to be plugged in. You can have
two 1551 drives, two 1541 drives, and two printers hooked up to the
computer at once as long as each peripheral is assigned a different
device number. When there is a contention with duplicate device
numbers, the 1551 has priority over the 1541.
Memory map of the 1551:
Location Purpose
$0000-0001 8 bit port - 6510T
$00 : cpu data direction register
$01 : cpu port register
bit 0: drive head stepper 0 (STP)
bit 1: drive head stepper 1 (STP)
bit 2: drive motor on/off (MTR)
bit 3: drive LED (ACT)
bit 4: write protect sensor (WPS)
bit 5: density select #0 (DS0)
bit 6: density select #1 (DS1)
bit 7: byte latched (1 - yes, 0 - no)
$0002-00ff Zero page work area, *job queue, variables
$0100-01ff GCR overflow area and stack
$0200-02ff Command buffer, parser, tables, variables
$0300-06ff 4 data buffers, 0-3
$0700-07ff BAM resident in memory
$4000-4007 6523a I/O to computer controller
$c000-ffe5 16KB ROM, DOS and controller routines
$ffe6-ffff JMP table, user command vectors
*job queue and HDRS offset by 2 bytes - starts at $0002
TIA 6523 - Triport Interface Adapter
The TIA6523 is a tri-port adapter. It has 28 pins,
three data direction and three port registers. It's
mapped in at $4000-$4007 in the 1551. Some drives actually
contain a 6525 with a 6523 pinout.
Address 6523 TIA ($4000-$4007)
-------------------------------------------------------------------------------
0 Port A Data (data sent to the computer)
1 Port B Data (connected to the shift register of the R/W head)
2 Port C Data
bit 7: DAV (DAta Valid)
handshake from bit #6 from $FEF2/FEC2 of plus/4
bit 6: SYNC
0 -> SYNC found
1 -> no SYNC
bit 5: MODE (jumper)
drive number (0 -> 8, 1 -> 9)
bit 4: MODE (R/W head)
0 -> head in write mode
1 -> head in read mode
bit 3: ACK (ACKnowledge)
handshake to bit #7 of $FEF2/$FEC2
bit 2: DEV
1 -> drive mapped at $FEF0 on plus/4
0 -> drive mapped at $FEC0 on plus/4
bit 1: STATUS1 - mapped at $FEF1/FEC1 on plus/4
bit 0: STATUS0 - mapped at $FEF1/FEC1 on plus/4
01 Timeout during reading
10 Timeout during writing
11 End of data
Data direction registers ( 1 -> bit out, 0 -> bit in)
3 Port A Direction
4 Port B Direction
5 Port C Direction (set to $1F by the drive ROM)
6 N/A
7 N/A
User commands:
User command Function
u1 or ua Block read replacement
u2 or ub Block write replacement
u3 or uc Jump to $0500
u4 or ud Jump to $0503
u5 or ue Jump to $0506
u6 or uf Jump to $0509
u7 or ug Jump to $050c
u8 or uh Jump to $050f
u9 or ui Jump to ($fffa) reset tables
u: or uj Power up vector
The u1 and u2 commands are used to replace the Block-Read and
Block-Write commands, ui restarts the 1551 without changing variables,
uj cold-starts the 1551 almost as if it had been turned off and on
again.
Specifications of the 1551 disk drive:
Storage:
Total formatted capacity 174848 bytes per diskette
Maximum sequential file size 168656 bytes per diskette
Maximum relative file size 167132 bytes per diskette
Records per file 65535
Files per diskette 144
Tracks per diskette 35
Sectors per track 17-21
Sectors per diskette 683 total
Sectors per diskette 664 free for data
Bytes per sector 256
Integrated circuit chips used:
6510T Microprocessor, I/O
6523A I/O
23128 16KB ROM
4016 2KB RAM
Gate array Controller circuit
Physical dimensions:
Height 97 mm
Width 200 mm
Depth 374 mm
Weight 10.5 kg
Electrical requirements:
Voltage US 100-120 VAC
Voltage export 220-240 VAC
Freq US 60 Hz
Freq export 50 Hz
Power used 25 Watts
Media:
5 1/4 inch diskette
This information was rewritten by Jan Sefcik from the Commodore 1551
Disk Drive User's Manual. The memory map and the description of the
TIA were provided by Attila Grosz in 2003. Edited by Marko Makela.
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