7th Apr 2021, 7:50 pm | #1401 |
Octode
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Re: Non-working Commodore PET 3016
OK - swapped. Is there a preference which replacement EPROM I should use?
Colin. |
7th Apr 2021, 7:52 pm | #1402 |
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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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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
7th Apr 2021, 7:55 pm | #1403 |
Octode
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Re: Non-working Commodore PET 3016
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7th Apr 2021, 8:03 pm | #1404 |
Octode
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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. |
7th Apr 2021, 8:03 pm | #1405 |
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Re: Non-working Commodore PET 3016
Has UE8 and UE9 been replaced?
Maybe check activity on UA5-6 and UA4-8. |
7th Apr 2021, 8:05 pm | #1406 |
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Re: Non-working Commodore PET 3016
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7th Apr 2021, 8:06 pm | #1407 | |
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Re: Non-working Commodore PET 3016
Quote:
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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7th Apr 2021, 8:10 pm | #1408 | ||
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Re: Non-working Commodore PET 3016
Okey dokey. On it.
Colin. Quote:
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7th Apr 2021, 8:12 pm | #1409 |
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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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7th Apr 2021, 8:14 pm | #1410 |
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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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7th Apr 2021, 8:18 pm | #1411 |
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Re: Non-working Commodore PET 3016
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7th Apr 2021, 8:27 pm | #1412 | ||
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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:
Last edited by ScottishColin; 7th Apr 2021 at 8:35 pm. |
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7th Apr 2021, 8:29 pm | #1413 | |
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Re: Non-working Commodore PET 3016
Quote:
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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7th Apr 2021, 9:56 pm | #1414 | |
Octode
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Re: Non-working Commodore PET 3016
Quote:
So the Daver2 diagnostic, that replaces the EDIT ROM, boots slightly-differently and needs the proper (& working!) Kernal ROM fitted. |
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7th Apr 2021, 10:19 pm | #1415 | |
Octode
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Re: Non-working Commodore PET 3016
Quote:
- 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 10:25 pm. |
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7th Apr 2021, 11:44 pm | #1416 |
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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). |
8th Apr 2021, 12:06 am | #1417 | |
Octode
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Re: Non-working Commodore PET 3016
Quote:
Code:
INFINITE JMP INFINITE |
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8th Apr 2021, 1:59 am | #1418 | |
Octode
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Re: Non-working Commodore PET 3016
Quote:
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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8th Apr 2021, 2:35 am | #1419 |
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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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8th Apr 2021, 4:31 am | #1420 | |
Octode
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Re: Non-working Commodore PET 3016
Quote:
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 4:40 am. |
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