Posted By
Retroshire
on 2020-12-22
15:55:19
|  1551 > monitor by directory command
After giving in the directory command, my 1551 goes to machine language mode (like giving the monitor command).
Is this a known problem? Like a PLA problem or something like that?
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Posted By
siz
on 2020-12-22
16:12:36
| Re: 1551 > monitor by directory command
I don't understand what you want to say. The 1551 can't enter monitor mode as it has no such a thing.
You mean you have a 1551 connected to your computer and after executing a directory command you computer enters monitor? Or what?
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Posted By
Retroshire
on 2020-12-22
16:53:42
| Re: 1551 > monitor by directory command
correct
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Posted By
siz
on 2020-12-22
17:24:38
| Re: 1551 > monitor by directory command
Does it display anything else? For example BREAK message? If yes what are the register contents? Especially the first one (PC) which is the first 4 digits hexadecimal number in the monitor startup message.
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Posted By
Retroshire
on 2020-12-27
11:45:04
| Re: 1551 > monitor by directory command
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Posted By
SVS
on 2020-12-28
15:06:03
 | Re: 1551 > monitor by directory command
It seems to be a problem opening the logical file for Directory read.
Try these commands:
SYS DEC("EF08")
DIRECTORY U8
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Posted By
Retroshire
on 2020-12-28
15:22:27
| Re: 1551 > monitor by directory command
Thank you SVS for your suggestion. It does not result in function, again various breaks. Seem very different without cohesion.
Found out that there is also no activity in red light/stepmotor. The other motor turns by switching on and stops after some seconds. So that seems normal.
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Posted By
siz
on 2020-12-28
16:50:45
| Re: 1551 > monitor by directory command
@Retroshire: in a proper working plus/4 there can't be a break at that point of the KERNAL. I would try to replace the KERNAL ROM or the PLA from a working machine. KERNAL ROM is U24 in a plus/4 and the PLA is U19.
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Posted By
Retroshire
on 2020-12-30
04:20:56
| Re: 1551 > monitor by directory command
@siz perhaps a relavant detail: on the serialport the 1541 functions without problems. In case of a bad PLA or ROM this should have effect on the function of serial/1541, shouldn't it?
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Posted By
softice
on 2020-12-31
07:18:50
| Re: 1551 > monitor by directory command
I was thinking about this issue: doesn't the 1551 interface function as a cartridge, e.g., to reprogram the response to any disc accesses so the OS communicates with the parallel interface instead of the usual serial interface?
So maybe there is a ROM on the interface that is faulty? Or perhaps carefully clean the whole connector (on both ends) with isopropyl alcohol or something similar and try again?
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Posted By
gerliczer
on 2020-12-31
08:35:28
| Re: 1551 > monitor by directory command
The 1551 paddle has only an address decoder and the parallel port. No ROM of any kind there. TCBM protocol routines are all in the KERNAL. The really interesting thing is that the crash seemingly occurs in a place where there shouldn't happen anything like that. And that's baffling.
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Posted By
SVS
on 2020-12-31
12:18:34
| Re: 1551 > monitor by directory command
I suppose that (unfortunately) it could be the paddle...
It is a critical component of the 1551. Years ago, when I've bought 2 1551s from Germany, one of them was not running. After tested all, it was the paddle. The seller sent me a spare paddle and all went OK.
After so many years I don't remember what was the behavior of the 1551 with the fault paddle, but maybe it replied with unpredictable data on the port and the system exits with that message.
siz is right when says that the ROM does not allow to halt at this address, the first $00 that could Break the CPU is not near from that address.
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Posted By
Retroshire
on 2021-01-06
06:10:44
| Re: 1551 > monitor by directory command
Strange observation: on my C16 it does not give a break but 'device not present'.
Both, my C16 and Plus/4 are running with a replacement CPU of Piotr Bugaj (FPGA). The C16 has also a PLA replacement (on eprom).
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Posted By
Doug
on 2021-01-06
08:30:05
| Re: 1551 > monitor by directory command
If you're seeing a BRK at a location in ROM that is clearly not a BRK, this points to something (OK, the 1551) pulling the data bus low. Hence the CPU fetches 0x00 (BRK), rather than the correct instruction. It must be marginal on timing, since the system is clearly 'alive' - if the data bus was genuinely held low nothing would work (no display, nothing).
Not that any of this helps you debug it! 
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Posted By
Retroshire
on 2021-03-07
16:03:00
| Re: 1551 > monitor by directory command
I tried another Paddle from a working 1551: problem solved. So something in my paddle is broken. I try to replace the PLA with the PLAdvanced replacement.
OK: another strange observation >
FPGA CPU replacement (Piotr Bugaj) in C16: device not found error
Stock CPU in C16: no problem with 1551
IS THE FPGA CPU REPLACEMENT OF PIOTR BUGAJ COMPATIBLE WITH 1551 DISKDRIVE????
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