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Old 7th Apr 2021, 6:50 pm   #1401
ScottishColin
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Default Re: Non-working Commodore PET 3016

OK - swapped. Is there a preference which replacement EPROM I should use?

Colin.
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Old 7th Apr 2021, 6:52 pm   #1402
julie_m
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Default Re: Non-working Commodore PET 3016

Unless I am mis-reading the diagram, UI10 and UI11 are not part of the screen memory path. They are required between the DRAM data pins and the data bus to avoid anything being imposed on the bus during refreshing (the 4116 RAM chip has no separate output enable).
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Old 7th Apr 2021, 6:55 pm   #1403
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ScottishColin View Post
OK - swapped. Is there a preference which replacement EPROM I should use?

Colin.
I think Slothieís as it was failing at zero page and Iím not sure the other software reached zero page testing.
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Old 7th Apr 2021, 7:03 pm   #1404
ScottishColin
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Default Re: Non-working Commodore PET 3016

Well that was fun and didn't take long, but I still get the same screens/error messages with either Slothie's EPROM or Daver3 EPROM inserted as before.

The only slight difference is with the first two boots with Slothies EPROM inserted, I get zero page error - stopped, a blank screen, and then the same error message. The third reboot onwards, it's just a constant error message with no blanking of screen.

Colin.
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Old 7th Apr 2021, 7:03 pm   #1405
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Default Re: Non-working Commodore PET 3016

Has UE8 and UE9 been replaced?

Maybe check activity on UA5-6 and UA4-8.
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Old 7th Apr 2021, 7:05 pm   #1406
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Default Re: Non-working Commodore PET 3016

UE7 and UE8 have new sockets and new ICs. Not UE9 though.

Colin.


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Has UE8 and UE9 been replaced?

Maybe check activity on UA5-6 and UA4-8.
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Old 7th Apr 2021, 7:06 pm   #1407
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Default Re: Non-working Commodore PET 3016

Quote:
UI10 and UI11 are not part of the screen memory path
Exactly right Julie, I meant UE9 and UE10 - not the first time I've mixed those up with something else. UE9 - UE10 are the ones which sit in the read path from both the screen RAM and the system RAM. I am sure those have not been replaced, as Colin just seems to have confirmed.

Colin, may as well put R41 / R42 back as they were. If you want something to occupy you in the meantime then, if you feel like doing it, replace UE9 and UE10. I know you already have the ICs.
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Old 7th Apr 2021, 7:10 pm   #1408
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Default Re: Non-working Commodore PET 3016

Okey dokey. On it.

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Quote:
UI10 and UI11 are not part of the screen memory path
Exactly right Julie, I meant UE9 and UE10 - not the first time I've mixed those up with something else. UE9 - UE10 are the ones which sit in the read path from both the screen RAM and the system RAM. I am sure those have not been replaced, as Colin just seems to have confirmed.

Colin, may as well put R41 / R42 back as they were. If you want something to occupy you in the meantime then, if you feel like doing it, replace UE9 and UE10. I know you already have the ICs.
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Old 7th Apr 2021, 7:12 pm   #1409
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Default Re: Non-working Commodore PET 3016

Actually that might be better to verify activity at UE9-19 and UE10-19 instead of UA5-6, just in case the signal doesn’t reach its destination.
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Old 7th Apr 2021, 7:14 pm   #1410
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Default Re: Non-working Commodore PET 3016

We'll let Colin replace those UE9 - UE10 buffers and then at least there will be one less unknown.
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Old 7th Apr 2021, 7:18 pm   #1411
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Originally Posted by SiriusHardware View Post
We'll let Colin replace those UE9 - UE10 buffers and then at least there will be one less unknown.
Might have been better to check the control signals looked right first, but maybe too late now.
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Old 7th Apr 2021, 7:27 pm   #1412
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Default Re: Non-working Commodore PET 3016

I have two replacement ICs but no 2 x 20 turned pin sockets so I'll hold off this work for now - I'll order them tonight though. I expect they'll be with me end of the week.

*** EDIT - resistors R41/R42 have been put back ***

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Quote:
UI10 and UI11 are not part of the screen memory path
Exactly right Julie, I meant UE9 and UE10 - not the first time I've mixed those up with something else. UE9 - UE10 are the ones which sit in the read path from both the screen RAM and the system RAM. I am sure those have not been replaced, as Colin just seems to have confirmed.

Colin, may as well put R41 / R42 back as they were. If you want something to occupy you in the meantime then, if you feel like doing it, replace UE9 and UE10. I know you already have the ICs.

Last edited by ScottishColin; 7th Apr 2021 at 7:35 pm.
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Old 7th Apr 2021, 7:29 pm   #1413
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Default Re: Non-working Commodore PET 3016

Quote:
Might have been better to check the control signals looked right first, but maybe too late now.
Did we not already do that, hundreds of posts back? I'm sure there was a point where we did spend time on those buffers but at the time we couldn't really pin anything on them.

The suspicion that reads from both the display RAM and the system RAM are bad has only really arisen since we had the Daver2 test code to try, and the UE9 and UE10 buffers are in the read path from both.

If you do want to re-check the pin 1 / pin 19 signals on UE9 / U10 Slothie's rev c test code will make that easier as it will spend a lot of time writing as well as reading.
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Old 7th Apr 2021, 8:56 pm   #1414
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by Slothie View Post
Quote:
Originally Posted by ScottishColin View Post
And while I'm waiting for the EPROM, is it possible for someone to either explain to me how the code on the EPROM is called at boot? or is there a website I should go look at?

I'm interested in how the code is called in the first place.

Colin.
The EPROM is mapped into memory from addresses F800-FFFF. When a 6502 processor is reset, it looks in locations FFFC and FFFD for the address of the boot code. The EPROM has these locations programmed to the start of the diagnostics at F800! The original kernal ROM obviously had different code locations and therefore values in FFFC & FFFD but the principle is the same.
And just to complicate matters, the original (Not always socketed) Kernal ROM jumps to the (Country-specific, usually socketed) Edit ROM at $E000, after a small amount of processing (i.e. maskable interrupts have been inhibited and the decimal arithmetic flag cleared).
So the Daver2 diagnostic, that replaces the EDIT ROM, boots slightly-differently and needs the proper (& working!) Kernal ROM fitted.
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Old 7th Apr 2021, 9:19 pm   #1415
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by ScottishColin View Post
Well that was fun and didn't take long, but I still get the same screens/error messages with either Slothie's EPROM or Daver3 EPROM inserted as before.

The only slight difference is with the first two boots with Slothies EPROM inserted, I get zero page error - stopped, a blank screen, and then the same error message. The third reboot onwards, it's just a constant error message with no blanking of screen.

Colin.
Well at least trying this has shown that the reason the main RAM's Zero page is not working is not just down to one or more of the lower bank RAM(s) being faulty, with all the RAM IC's in the upper bank actually still OK.
- But still not necessarily that there are faulty ones in both banks (as could well be problems elsewhere, as well or instead)

However, if Commodore have (rather unusually when virtually all other similar computers would have used bidirectional buffers) used separate read-back buffers from both RAM's, then (knowing how many others buffers this PET seems to have devoured so far) it does seem that these could well be highly-suspect.
And it may be possible to confirm this, by 'scoping the input and output sides (or maybe just outputs and enable), with the firmware continually trying to read from memory.
I think the first-version Slothie diagnostics one you have halts, but the Daver2 one should continually loop in the screen RAM test (although looking at the code it will do 2048 bytes writes, but only 1 read will be done if this doesn't match write value and it then repeats the 2048 bytes writes again). So should be easier to see with the new updated Slothie one.
So I'll leave it upto Sirius, to specify exactly what to do, if he thinks there's some merit in trying this.

Last edited by ortek_service; 7th Apr 2021 at 9:25 pm.
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Old 7th Apr 2021, 10:44 pm   #1416
SiriusHardware
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Default Re: Non-working Commodore PET 3016

Colin seems so much more confident now about removing and replacing ICs that I think the path of least difficulty / greatest speed is just to replace UE9 / UE10 so that we know for sure they are OK.

However, Colin's not going to be able to do that until he gets the sockets so there will be a window of opportunity for anyone curious enough to want to have a look at the data traffic generated by Slothie's test code Rev c. passing (or failing to pass) through the original buffers.

As always, please try to break requests for any such measurements down into individual steps with the test points referred to by IC circuit number / (Pin number).
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Old 7th Apr 2021, 11:06 pm   #1417
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ortek_service View Post
I think the first-version Slothie diagnostics one you have halts.
Being picky, it doesn't halt (not sure a 6502 can...) but its in an infinite loop:
Code:
INFINITE   JMP INFINITE
So the processor will just be fetching the jump instruction and its 2 byte argument continuously from the ROM.
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Old 8th Apr 2021, 12:59 am   #1418
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Default Re: Non-working Commodore PET 3016

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Being picky, it doesn't halt (not sure a 6502 can...) but its in an infinite loop:
Code:
INFINITE   JMP INFINITE
So the processor will just be fetching the jump instruction and its 2 byte argument continuously from the ROM.
Yes, I did mean that this firmware would appear to stop and wouldn't proceed any further - rather than the endless-loop jumping much further-back to re-attempt writing / reading of the RAM (So meaning those lines could be probed with 'scope etc).

As the 6502 uP lacks HALT (until Interrupt) instruction of the Z80 etc. (or any Sleep modes of more modern uC's).
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Old 8th Apr 2021, 1:35 am   #1419
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Default Re: Non-working Commodore PET 3016

With the daver2 test running, which seems to be continuously retrying screen ram test, check for activity on UE9-19 and UE10-19.
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Old 8th Apr 2021, 3:31 am   #1420
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With the daver2 test running, which seems to be continuously retrying screen ram test, check for activity on UE9-19 and UE10-19.
(And original Kernal ROM refitted, for daver2 EPROM that to work in Edit-ROM position)
In particular, need to check that these (connected together, so should give the same reading) both go Low.
As when this RD signal is high, then UA4 NAND-gate Inverts it to produce WR (For UE9-1 & UE10-1) - which must have gone low OK for the writing to screen memory via these to work.

Checking that all six 74LS244 Memory Write & Read buffers are actually passing data correctly in read mode is a bit more involved, when they are connected-up to be able to pass data both ways, so need to check RD input at the same time as Outputs to CPU.

I can't really see why Commodore couldn't have done all of this with just two 74LS245 (Direction-selectable) Tristate buffers, rather than effectively making these from pairs of 74LS244's and then cascading a CPU-side pair with pairs on the Main & Screen RAM's. Seems like a lot more ones to possibly fail!

Last edited by ortek_service; 8th Apr 2021 at 3:40 am.
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