Commodore PET 2001-8 Question

[dondi]

Results with spare 6520

 

[daver2]

OK, so that's fixed the IEEE488 port.

Not sure what the four BAD test lines indicates on the right-hand side?

I will check the VOSSI manual and code.

Dave

 

[dondi]

It does

 

[dondi]

It appears to be the missing RAM?

 

[daver2]

Just worked that out now!

Yes, so that is all good now (apart from ROM F).

Dave

 

[daver2]

Let's call it a night now and have a think about the ROM 'F' issue.

I am thinking of removing your 'C' ROMs from H1 and H5 and transplanting the F0 ROM (H4) into C0 (H1) and transplanting the F8 ROM (H7) into C8 (H5) and then running the VOSII tester.

It will complain (!) because the ROM checksums are incorrect but (hopefully) it will display the checksums so we can check them manually.

Nivag, what do you think?

Dave

 

[daver2]

The VOSSI ROM source code does not contain the checksums for the F8 (H7) ROM. So scratch that one for now.

We can still test the F8 ROM (H4) though.

Remove the C0 ROM from H1 and transplant the F0 ROM from H4 into H1 and test using VOSSI.

If the ROM is working, The C0 (H1) ROM should give us a checksum of either $12 (ROM -16) or $89 (ROM -25).

Just be careful with removing and inserting the ROMs...

Dave

 

[Nivag Swerdna]

Using VOSSI for the 2K ROM test is a good idea. The checksum isn't very robust... I think it is a bit weird... but it should match if they do perfectly match. Might match even if they don't.

2K checksums in PETTESTER might be nice

checksum_11 = $4b ; rom checksums with carry
checksum_12 = $e6
checksum_13 = $32
checksum_14 = $6b
checksum_15 = $60
checksum_16 = $12
checksum_18 = $a6
checksum_19 = $b6
checksum_20 = $ed
checksum_21 = $89
checksum_22 = $9c
checksum_23 = $25
checksum_24 = $c0
checksum_25 = $89
checksum_26 = $93

I assume 16 and 18 are relevant here.

 

[daver2]

I get 16 and 25?

Dave

 

[daver2]

>>> 2K checksums in PETTESTER might be nice.

I'll put that on the list...

Dave

 

[dondi]

I swapped H1 and H4. Hope that is what you meant.

Anyway, here is the result

 

[Nivag Swerdna]

I get 16 and 25?

Dave

I wrote a quick program...

rom-1-c000.901439-01.bin 0x4b
rom-1-c800.901439-05.bin 0xe6
rom-1-d000.901439-02.bin 0x32
rom-1-d800.901439-06.bin 0x6b
rom-1-e000.901439-03.bin 0x60
rom-1-f000.901439-04.bin 0x12
rom-1-f800.901439-07.bin 0xa6
rom-2-c000.901439-09.bin 0xb6
rom-3-c000.901439-13.bin 0xed
rom-3-c800.901439-14.bin 0x89
rom-3-d000.901439-15.bin 0x9c
rom-3-d800.901439-16.bin 0x25
rom-3-e000.901439-17.bin 0xc0
rom-3-f000.901439-18.bin 0x89
rom-3-f800.901439-19.bin 0x93

sum = 0
carry = 0
for i in range(0, len(data)):
x = data
sum = sum + x + carry
carry = 1 if sum>255 else 0
sum = sum % 256
if carry > 0:
sum = sum + carry
sum = sum % 256

Not sure I really approve of the algorithm... but it does produce a number.

 

[Nivag Swerdna]

12 is rom-1-f000.901439-04.bin aka 6540-016... something you would expect to find in H4 and service F000-F7FF.. one looks good*
We are looking for an A6

*ah... that was probably substituted! doh

 

[daver2]

So $EF doesn't match any of the checksums that Nivag has just posted - so that ROM in H1 is likely duff.

Dave

 

[dondi]

What do we do about that?

 

[daver2]

Remove the ROM from H1 (duff F0) and move the ROM from H7 (F8) into H1 now and re-run VOSSI.

By the way, I meant to remove the ROM that was originally in H1 and put it safely to one side.

>>> What do we do about that?

You either try and purchase a replacement ROM, or you ask Nivag for a replacement ROM board pre-programmed with a new one...

Let's see if you need two (2) replacement ROMs first!

Dave

 

[Nivag Swerdna]

You either try and purchase a replacement ROM, or you ask Nivag for a replacement ROM board pre-programmed with a new one...

You could... but there are probably cheaper alternatives if you aren't too worried about aesthetics. You can get a ROM adapter for a more commonly available ROM and find a friend in your region who would program for you.
Maybe I should try and change my design to be black with the bits on the bottom. I think the person who sold you the RAM might also do ROMs? (I see some ROMs in their website... it's worth asking)

 

[dondi]

Configuration and result

 

[daver2]

So something is not right there. It looks like you have put the C0 ROM back into H1.

I am getting a bit tired now. Perhaps we had better call it a day?

Are all of your ROMs back in the correct sockets (as you posted ages ago)? With the exception of H4 (that is empty because it is likely duff).

I think we have all done pretty well today with this PET repair! We are on track...

Dave

 

[dondi]

We'll continue tomorrow. Good night!