[Techtoolslist] Noise…

[Kevin Moore]

Very nice! I do tend to stay away from RD boards, but this is good info to
have.

Kevin


On Mon, Oct 9, 2023 at 12:27 AM John Robertson via Techtoolslist <
techtoolslist at flippers.com> wrote:

> I was trying to sort out a Rottendog System 9TO11 MPU that would work with
> some EPROMs - sometimes - but not others.
>
> So pulled out the 9010 and 6802 pod and did some signatures.
>
> Sure enough the signatures were not the same ones twice.
>
> Made a simple RAM test for verifying the Data and lower Address lines at
> the EPROM positions - used a 6265 RAM and tied the /WE line to pin 27 of
> the CMOS RAM (R/W).
>
> And the 9010 RAM tests worked just fine so I was sure the Data lines and
> lower Address lines (A0-A12) were good.
>
> Scope on A13 and A14 were inconclusive.
>
> Pulled out my 6802 NOP CPU (hard wired to NOP) and scoped A13 - lots of
> noise on the bottom half of the cycle!
>
> Replaced the 74HCT244 buffer and the board is again a happy camper!
>
> I do like my NOPs for checking Address lines!
>
> I made them years ago for the common 8-bit CPUs and use them periodically
> on weird problems that the Fluke 9010 can’t nail down. Just bend the CPU’s
> Data leads up and tie them as needed to produce the NOP code.
>
> John :-#)#
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