Page 3 of 5

Re: 600D Colour RAM. Help!!!!

Posted: Thu May 09, 2019 1:57 pm
by waltermixxx
MK14HAK wrote: Thu May 09, 2019 9:44 am No problem here folks. Original RevD always reads $D400-D7FF top nibble as $D. Low nibble is whatever you poke it. RUN multiple times same result. (Z=0 on completion) Only no colour :mrgreen:

Address decoding ??? I wonder if the memory test program might give a clue?
Your result's are based on the Original OSI 600 REV. D, not the remake, did I read that correctly?
if so then we need some folks who built the REV. D remake to compare notes. :)

Thank you for running the test.

Re: 600D Colour RAM. Help!!!!

Posted: Thu May 09, 2019 1:59 pm
by froso
Hi again, I saw the video and, the two suspects are the 8T28 and the 2114. change one of them and repeat the test, and then the other. It can be a break trace or a bad soldered, but I doubt it.

Re: 600D Colour RAM. Help!!!!

Posted: Thu May 09, 2019 2:13 pm
by waltermixxx
I was thinking also swapping out or changing U20 (74LS138) and U79 (74LS86), if there is a significant propagation delay on U79 the write pulse may not be there in time? I will see if I have another 7486 or LS86, currently using a 74LS86. I will swap around my 8T28's as well as it couldnt hurt.

Re: 600D Colour RAM. Help!!!!

Posted: Thu May 09, 2019 2:56 pm
by Steve Gray
MK14HAK wrote: Thu May 09, 2019 9:44 am No problem here folks. Original RevD always reads $D400-D7FF top nibble as $D. Low nibble is whatever you poke it. RUN multiple times same result. (Z=0 on completion) Only no colour :mrgreen:

Address decoding ??? I wonder if the memory test program might give a clue?
Thanks for testing! It's good to hear that the original RevD works. Anyone with a clone want to try?

I guess Walter and I have to figure out if there is a bad chip, bad socket, or bad solder joints...

I'm still going to complete the colour circuit and make a board, so hold tight! ;-)

Steve

Re: 600D Colour RAM. Help!!!!

Posted: Thu May 09, 2019 11:47 pm
by Klyball
I have had problems mixing up 8t26 and 8t28

Re: 600D Colour RAM. Help!!!!

Posted: Fri May 10, 2019 2:32 am
by MK14HAK
Hold the phone... This is weird, today I am getting the same problem. Hi nibble is constant $D but lo nibble is now random. I thort it may be the BASIC program and tried a few variations but now still have errors.
Using the Cegmon monitor and tabulating memory repeatedly: TD7A0,D7FF shows random read errors!
Starts to look like a timing issue? Steve are seeing colour changes at random after you have filled all memory with the one colour?

Re: 600D Colour RAM. Help!!!!

Posted: Fri May 10, 2019 3:44 am
by waltermixxx
Klyball wrote: Thu May 09, 2019 11:47 pm I have had problems mixing up 8t26 and 8t28
we are only using 8T28's on the 600 REV. D. :)

Re: 600D Colour RAM. Help!!!!

Posted: Fri May 10, 2019 3:47 am
by waltermixxx
MK14HAK wrote: Fri May 10, 2019 2:32 am Hold the phone... This is weird, today I am getting the same problem. Hi nibble is constant $D but lo nibble is now random. I thort it may be the BASIC program and tried a few variations but now still have errors.
Using the Cegmon monitor and tabulating memory repeatedly: TD7A0,D7FF shows random read errors!
Starts to look like a timing issue? Steve are seeing colour changes at random after you have filled all memory with the one colour?
once written (as far as I remember), they dont change, for instance, if Steve is writing 15 to all the memory locations then instead of the colour associated with 15 being set, it will be some random colour (like the random number the program generates). Once written it does not randomly change. it's the value when written that gets messed up. :) Steve can confirm, but pretty darn sure that is the case. :)

Re: 600D Colour RAM. Help!!!!

Posted: Fri May 10, 2019 9:13 am
by MK14HAK
Agreed U79 LS86 looks a possibility here. I only had one other amongst my spares and swapped it but no improvement. Its involved with a few timing signals and I note it is one of the few socketed TTLs on my original RevD.Could have been a select on test component. I wonder if a few pFs cap might help ? ( I also tried 550ns RAM and 4 different manufacturers 8T28s )

10 C=208
20 FOR X=54272TO55295
30 POKEX,C
40 NEXT
50 FOR X=54272TO55295
60 B=PEEK(X)
70 IF B<>C THEN Z=Z+1:PRINTC;"PEEK ";X;"=";B
80 NEXT
90 PRINTZ;"ERRORS";:PRINT" C=";:PRINTC
95L=C
100Z=0:INPUT" C";C
110IFC=0THEN STOP
115IFC=1THEN C=L:GOTO50:rem read test
120GOTO20

Entering values 223 and 208 at input prompt.($D0,$DF) Entering 1 loops on a read test. I get what appears to be both write and read errors. With not so may read errors.These appear at different locations each time you loop the read test which is understandable if this is a timing issue.

Re: 600D Colour RAM. Help!!!!

Posted: Fri May 10, 2019 12:15 pm
by Steve Gray
waltermixxx wrote: Fri May 10, 2019 3:47 am
MK14HAK wrote: Fri May 10, 2019 2:32 am Hold the phone... This is weird, today I am getting the same problem. Hi nibble is constant $D but lo nibble is now random. I thort it may be the BASIC program and tried a few variations but now still have errors.
Using the Cegmon monitor and tabulating memory repeatedly: TD7A0,D7FF shows random read errors!
Starts to look like a timing issue? Steve are seeing colour changes at random after you have filled all memory with the one colour?
once written (as far as I remember), they dont change, for instance, if Steve is writing 15 to all the memory locations then instead of the colour associated with 15 being set, it will be some random colour (like the random number the program generates). Once written it does not randomly change. it's the value when written that gets messed up. :) Steve can confirm, but pretty darn sure that is the case. :)
Correct. Some bytes are written with the wrong value and to the wrong location, but they do not change when no longer writing to colour memory.

Steve