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Commodore PET 2001 with no cursor
- Thread starter richterh
- Start date
daver2
10k Member
Well done Harald, you are getting there...
The MEM FAIL message indicates a RAM fault of some description...
The page 0/1 tests are a 'quick and dirty' test of the first 512 bytes of RAM. This memory test is a much more thorough test of all of the RAM. It is indicating the odd problem.
I also see the odd 'random' character on the screen. This is unexpected behaviour.
There is a possibility that the 'quick and dirty' page 0/1 RAM test lets the odd fault through - just for the more thorough memory test to fail in unexpected ways. This is one reason I am improving the page 0/1 test in Version 5.
The ROM and keyboard test I was talking about occurs prior to this test incidentally. It is a screen with a counter that counts down to zero before moving on to this MARCH-C memory test.
Dave
The MEM FAIL message indicates a RAM fault of some description...
The page 0/1 tests are a 'quick and dirty' test of the first 512 bytes of RAM. This memory test is a much more thorough test of all of the RAM. It is indicating the odd problem.
I also see the odd 'random' character on the screen. This is unexpected behaviour.
There is a possibility that the 'quick and dirty' page 0/1 RAM test lets the odd fault through - just for the more thorough memory test to fail in unexpected ways. This is one reason I am improving the page 0/1 test in Version 5.
The ROM and keyboard test I was talking about occurs prior to this test incidentally. It is a screen with a counter that counts down to zero before moving on to this MARCH-C memory test.
Dave
richterh
Member
Yes, the ROM and Keyboard test has run except with the I1 RAM
Attachments
daver2
10k Member
It might have run - but it is not running correctly!
1. You have an extraneous '@' character at the end of the character test. This cell should be occupied by a hex value of $20 - but an '@' is a hex value of $00. This seems to be a similar issue to the full memory test extraneous character I saw. This could indicate that one of the VIDEO RAMS (the low data bits) is just on the edge somewhere - or has a single faulty memory cell. My test program doesn't perform exhaustive tests due to the space constraints.
2. The keyboard values are all $82 - they should be all $00. Have you got the keyboard PIA removed by any chance?
3. The ROM checksums do not look correct. The 'C' ROM is fine for BASIC 1/2. The 'B' and 'D' ROM checksums don't match what I have previously seen. That doesn't mean they are wrong - you may have a set of ROMs we have never seen before. It could also mean that one of the B or D ROM pair are faulty as well... The 'F' ROMs have a checksum that appears to match BASIC-4?
Dave
1. You have an extraneous '@' character at the end of the character test. This cell should be occupied by a hex value of $20 - but an '@' is a hex value of $00. This seems to be a similar issue to the full memory test extraneous character I saw. This could indicate that one of the VIDEO RAMS (the low data bits) is just on the edge somewhere - or has a single faulty memory cell. My test program doesn't perform exhaustive tests due to the space constraints.
2. The keyboard values are all $82 - they should be all $00. Have you got the keyboard PIA removed by any chance?
3. The ROM checksums do not look correct. The 'C' ROM is fine for BASIC 1/2. The 'B' and 'D' ROM checksums don't match what I have previously seen. That doesn't mean they are wrong - you may have a set of ROMs we have never seen before. It could also mean that one of the B or D ROM pair are faulty as well... The 'F' ROMs have a checksum that appears to match BASIC-4?
Dave
richterh
Member
Doesn't sound good to me, some RAM and ROMs may be buggy and we're still searching…
daver2
10k Member
You just have to work the problem through a step at a time.
I have just been reviewing your thread from the beginning and note that you had the strange character on the screen back in post #1. I suspect this is one bad memory cell in one of the video RAMs.
If you are running my PETTESTER from the ROMulator that accounts for the BASIC-4 'F' ROM. You need a working Kernal ROM in this particular emulator to get my PETTESTER running.
So yes, it looks like you still may have some ROM, RAM and a bit of video RAM to work through. But you can do it!
Dave
I have just been reviewing your thread from the beginning and note that you had the strange character on the screen back in post #1. I suspect this is one bad memory cell in one of the video RAMs.
If you are running my PETTESTER from the ROMulator that accounts for the BASIC-4 'F' ROM. You need a working Kernal ROM in this particular emulator to get my PETTESTER running.
So yes, it looks like you still may have some ROM, RAM and a bit of video RAM to work through. But you can do it!
Dave
ajgriff
Experienced Member
Agreed but where next? Lots of choice. I'd concentrate on the RAM chips first. In original configuration the PET only needs six working RAM chips in order to boot. With those in positions I1, J1, I2, J2, C3 & C4 it should display the screen in the attached photo. If Harald can get his machine to this point it should then be possible to address other issues using the ROMulator and PETTester with Dave's guidance.
Alan
daver2
10k Member
+1.
Sorry, my works internet connection died...
I forgot that IT was taking the internet down after work (so to speak).
I am at home now...
Dave
Sorry, my works internet connection died...
I forgot that IT was taking the internet down after work (so to speak).
I am at home now...
Dave
dave_m
Veteran Member
From my review of the ROM checksums, I agree with daver, at least one of the 'D' ROMs (6540-013 and 6540-014) is bad. We can't tell which one as we only have PETTEST 4K checksum to compare the two 2K ROMs.
The 'F' ROM must be from the ROMulator so we do not know the condition of the Harald's ''F' ROMs (6540-016 and 6540-018). Also of course we do not know the condition of the Editor 'E' ROM (6540-015).
And there is no 'B' ROM in the 2001-8 configuration.
daver2
10k Member
>>> And there is no 'B' ROM in the 2001-8 configuration.
Hmm, I forgot about that...
Dave
Hmm, I forgot about that...
Dave
richterh
Member
ajgriff
Experienced Member
Setting aside PETTester for a moment, what happens if the ROMulator is set so that the PET uses 6 good 6550s and the ROMulator just provides a suitable ROM image thus overriding the PET's own ROMs?
Alan
Alan
daver2
10k Member
>>> but I just got a garbage screen like in the beginning.
By this do you mean with the PETs original ROMs?
If so, I suspect at least one of those ROMs to be faulty - and will mean that BASIC will not run as a result.
I think (with Bitfixer's help and/or documentation) you can configure the ROMulator to emulate the ROM but not the RAM - and try and get your machine to run natively with its own RAM.
I am still wondering about that pesky errant character on the screen though (Obsessive Compulsive Disorder kicking in here)...
Did you put the keyboard PIA in with my PETTESTER and test the keyboard out?
Dave
By this do you mean with the PETs original ROMs?
If so, I suspect at least one of those ROMs to be faulty - and will mean that BASIC will not run as a result.
I think (with Bitfixer's help and/or documentation) you can configure the ROMulator to emulate the ROM but not the RAM - and try and get your machine to run natively with its own RAM.
I am still wondering about that pesky errant character on the screen though (Obsessive Compulsive Disorder kicking in here)...
Did you put the keyboard PIA in with my PETTESTER and test the keyboard out?
Dave
richterh
Member
I will talk with bitfixer about the ROM emulation.
When I startet debugging I thought it was a good idea to use the ROMulator to make sure to have no RAM/ROM issues. Now I have this tool and still problems with it. Do not know why. I am a little confused.
Harald
When I startet debugging I thought it was a good idea to use the ROMulator to make sure to have no RAM/ROM issues. Now I have this tool and still problems with it. Do not know why. I am a little confused.
Harald
daver2
10k Member
Why are you confused?
If you use Bitfixer’s card to replace your RAM and ROM (as in your original post) then you appear to have a problem with some other PET logic that is not emulated (e.g. the video circuitry and the PIAs and VIA).
If you switch in my PETTESTER, you are using a BASIC-4 Kernal ROM and my PETTESTER (as part of the Bitfixer card) but the original PET RAM and remaining PET ROMs.
There is no point in switching in my PETTESTER code and not testing the PERs devices!
Dave
If you use Bitfixer’s card to replace your RAM and ROM (as in your original post) then you appear to have a problem with some other PET logic that is not emulated (e.g. the video circuitry and the PIAs and VIA).
If you switch in my PETTESTER, you are using a BASIC-4 Kernal ROM and my PETTESTER (as part of the Bitfixer card) but the original PET RAM and remaining PET ROMs.
There is no point in switching in my PETTESTER code and not testing the PERs devices!
Dave
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ajgriff
Experienced Member
I understand your frustration Harald but if you think back to the beginning of this thread we identified early on that they were/are logic problems on your PET's main board. Bitfixer's ROMulator wasn't designed to address such faults. In essence it allows you to run the PET using its own on board RAM and ROM images. We've subsequently established that the PET's main board also has faulty RAM(s) and ROMs. I think the best thing to do now is to correct the logic fault(s) first. You will then have a fully functioning PET when using the ROMulator's RAM and ROM images. You'll then have to decide how far you want to go in terms of fixing the main board's RAM and ROM faults. Stick at it!
Alan
dave_m
Veteran Member
Alan, I agree. Harald should test all his 6550 RAMs and use the good ones for the two video RAMs and keep the other good ones for video spares. The ROMulator will be perfect for ROM and 32K RAM as there are probably too many bad 6540 and 6550 memory chips to replace with adapters. Then we can fix the other problem of bad cursor, etc. The PET will be up and running in no time.
richterh
Member
Hi all,
you give new hope to me, thanks. I found 3 additional RAMs in an old spare part box. (I owned a PET in 1980 and got similar problems with it). Two of them seems to be good. I will test all RAMs to be sure they are good.
Harald
you give new hope to me, thanks. I found 3 additional RAMs in an old spare part box. (I owned a PET in 1980 and got similar problems with it). Two of them seems to be good. I will test all RAMs to be sure they are good.
Harald
ajgriff
Experienced Member
Good morning Harald. I wouldn't worry about testing all the RAMs for now. Just make sure that there are two good chips in the video RAM postions (C3 & C4), set the ROMulator to use its on board RAM & ROM and get back to the screen with the misbehaving cursor shown in the first photo of your opening post (#1). Daver2 and others will then help you resolve the cursor issue.
Having read the thread again I'm not too clear about what you did when you "exchanged the PIAs" to no effect. Did you fit two known good PIAs? Also back then did you try running the PET without the PIAs fitted? If so what happened?
Alan
Having read the thread again I'm not too clear about what you did when you "exchanged the PIAs" to no effect. Did you fit two known good PIAs? Also back then did you try running the PET without the PIAs fitted? If so what happened?
Alan
