Re: Programmer troubles with a new twist.

Cameron Rector wrote:
> Ok, I tried the pull-up resistor idea and there was no change.
>
> What I did find was address 800h contains the same data as 000h and 801h
> = 001h and so on. It appears that the programmer is resending the first
> half of the ram to 800h and above.
> I only checked the first 8 addresses and the data matches, so I assume
> that it continues.
> The programmer has internal memory and when I query 800h it has the
> correct data stored there.
>
> I looks like it programs the first 2048 in the bottom half of the eprom
> and then programs the first 2048 in the top half of the eprom.
>
> Anythoughts other than the trash can?

Pop it open and find out how the RAM is wired up. I'll bet it's going through
an LS245 or LS244. See if the A11 output is correct (trace it from the CPU to
the RAM; the RAM address lines might have been re-ordered to ease PCB layout).

If the buffers are socketed, swap 'em around! Get a known-good buffer chip
then swap it into each socket and re-test each time. When the fault
disappears, swap the 'dead' chip back in and see if the fault reappears. If it
does, you've found the problem.

Speaking of sockets, removing and re-seating any socketed ICs would also be a
good idea. Also check for dry joints on the PCB while you're in there.

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