VT101 8085 CPU Fault

Johnny Billquist bqt at update.uu.se
Sun Jan 18 16:53:27 CST 2015

On 2015-01-18 23:04, Diane Bruce wrote:
> On Sun, Jan 18, 2015 at 09:47:35PM -0000, Robert Jarratt wrote:
> ...
>>> you more. Nice sharp edges to signals when they shift. Times that look
>>> reasonable... Steady levels, and correct levels.
>> It will never be steady with a scope because the address lines won't be a regular waveform. That said they looked very different on the faulty board to how they looked on the good board.
> A remote possibility is the boot ROM is b0rked and it's simply running
> around like a chicken without a head.
> That is something a good logic analyser could tell you.

If the RD pin never gets active, the contents of the ROM will not even 
be presented to the CPU, so while it's possible the ROM is borked, that 
is not the problem we're trying to fix right now.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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