On Wednesday, 14 May 2014 at 04:45:41 UTC+10, Michael J. Mahon wrote:
retrogear <[email protected]> wrote:
*C600
returns
C600-A2
A2 is the first byte of the slot 6 disk card. That indicates it is reading the
rom address and data. I meant to type *C600L to get a listing of the rom something like this:
C600 A2 20 LDX #$20
C602 A0 00 LDY #$00
C604 A2 03 LDX #$03
C606 86 3C STX $3C
C608 8A TXA
C609 0A ASL A
C60A 24 3C BIT $3C
C60C F0 10 BEQ $C61E
C60E 05 3C ORA $3C
(and so on)
if it's reading the ROM like this then try:
*C600G
to execute the boot floppy code with the disk drive connected.
The motor should come on and the drive recalibrate. If no drive activity, and the card and drive are ok and connected correctly then I would think more like a power supply problem feeding the card to power the motor, etc. There are
+5 -5 +12 -12 supply lines feeding and if one is bad then I would think you could have a condition as you describe. Let me end this by saying I
do not have experience troubleshooting Apple II computers in particular but many years of troubleshooting electronics and pc's in general. So my advice is worth about
two cents :)
Larry
Or /DEVSEL could be missing, or...
If the rest of the machine works, including video, then power is almost certainly reaching the slots.
If power is not making it from the slot to the drive, there are connections on the card, a cable and two connectors, and the drive's select logic that could be an issue.
Under the rash assumption that no card, cable, or drive is killing other things, it is *extremely* helpful to isolate which subassembly is failing. This is easily done by swapping one element at a time in a working system: processor, disk controller, cable, and drive.
When you discover which subassembly "moves the fault", then you have (very likely) discovered which subassembly contains the fault.
If it's still the processor, then fault isolation can move to the next level--inside the processor.
If you can list the contents of the disk controller's ROM, then the address and data lines are working and /IOSELECT for the slot is working.
Of course, +5v is also working.
You can reference the MOTORON and MOTOROFF soft switches directly for the controller slot using the monitor. If they don't start and stop the motor, then any subassembly (above) could be bad. Isolating the failing
subassembly is critical.
--
-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
I'm not sure whether the original issue was resolved, but I had a similar issue myself. The unit (platinum //e) would turn on and boot straight to a prompt rather than trying to boot from floppy. I tested the various select signals with a logic probe (IO
select, device select, io strobe) and that all looked ok. On inspecting slot memory (C600L for example) however, I was frequently seeing incorrect bits in the upper nibble. This pointed to the 74LS245 bus transceiver being flaky as the data bus to the
CPU was all good - just slot data was affected. Replacing the 74LS245 resolved the problem.
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