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Commodore PET 2001-8 Question

Ah, that is TIM (the machine code monitor) running out of ROM.

This indicates that the CPU has executed a BRK instruction (opcode $00) or the keyboard PIA is not healthy. There is also a signal line (called DIAG) on the Keyboard PIA pin PA7. This pin is not normally connected - so TIM shouldn't be invoked.

We are still not out of the woods yet...

I think a little 'brainstorming' is now called for.

Can you type any characters on the keyboard at TIMs '.' prompt or not?

Dave
 
I wasn't able to type anything with the last screen, but I pressed RESET and got this screen
 

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Oh well, that is BASIC running!

It looks to have about the right amount of memory that you have fitted 4K minus a bit.

Keyboard next...

Does it work now?

Dave
 
I have also now worked out that the VOSSI 8-bit checksums are not compatible with my 16-bit checksums. That took me a while to work out why!

Dave
 
RAM jumper is OFF. Cursor flashing.

Keyboard is responsive and all keys appear to work although some need a little "prodding".

RESET produces same BASIC screen with flashing cursor.
 
FYI

1691171501100.png
@dondi This is what I see from the Photos.... You have what a lot of people would refer to as Basic 1r. That's the very original (and very buggy version) fixed by having -019 in H1 rather than -011. That's a very respectable early version.
 
So the 'key poking' requires a bit of key cleaning.

However, before you do this, you need to read the relevant threads within VCFED - otherwise you can do more damage than you fix!

Can you enter and run a simple BASIC program?

10 FOR I=1 to 10
20 PRINT "HELLO DONDI"
30 NEXT I

Dave
 
Well, it runs...

We could do with trying to find out why it didn't work last time (when we used the C, D and E ROMs from the PET and the F ROM from Nivag's RAMulator).

Perhaps it just needed a reset?

Either that, or I selected the wrong F ROM to emulate?

Nivag, any thoughts?

Dave
 
Since Nivag has mentioned BASIC 1r, and there is a BASIC 1r setting on the RAMulator, perhaps we should use that?

Note the link settings that you have now (just in case my assumptions are incorrect) so we can return to a working system.

Set the ROM Enable links to OFF OFF OFF ON. Just emulating the 'F' ROM.

Set the ROM Bank links to OFF OFF ON OFF. Select BASIC 1r.

Poke RESET...

Dave
 
Results from Post #132
 

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daver2 said:
Since Nivag has mentioned BASIC 1r, and there is a BASIC 1r setting on the RAMulator, perhaps we should use that?
Click to expand...
OFF OFF ON OFF should match what's on the board...

1691174536424.png

The numbering differences between the 6540- and 901439- markings is really confusing. The image a couple of posts back shows the equivalence.
 
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Success...

Right, last test for tonight... Unless you want to put your spare 6520 into the IEEE488 empty socket and give VOSSI another run to test the IEEE488 port.

Incidentally, my PETTESTER V5 will have the IEEE488 and USER port test code incorporated - along with the beeper (in later PETs). This will also test the VIA.

Can you just move link ROM Enable F from ON to OFF. This will use all of the 'real' ROMs again.

If this doesn't work - it clearly indicates that one (or both) of the F ROMs are faulty and we can look at that later.

Dave
 
OK, that clearly indicates that one (or both) of the H4 or H7 ROMs are faulty.

Put the link back again and make sure the PET still works.

Did you want to try your spare 6520 in the empty IEEE488 socket?

Dave
 
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