Just a general maybe way off the wall comment.
I have done this several times, and hand wired lots of z80s.
In every case where its a almost run, it is power. Have you put a scope on vcc and see
that its rock solid?
You describe a random case it fails at different points, this has to be either power to
cpu, or buffers and eproms not presenting the cpu with valid data.
There is no other cause, and a emulator wont help you find it.
This is hardware, look at, with 2 probes the buffered I/O on each bit (in, signal, out
signal). Brute force replace any buffer drivers. Who else is on the same wire, remove
any shared bussed devices, I hope they are sockets.
The problem that it is chip failures is almost zero.
It is power, a bad decouple cap somewhere, like when all address lines roll and the buffer
chip pulls a slug, sagging the rest down.
Look at all address and data lines on the scope, should be a clean cat eye with never a
trace in the middle or floating.
This is fun stuff, enjoy.
Date: Sat, 21 Feb 2009 21:02:24 -0500
From: robo58 at optonline.net
To: cctech at classiccmp.org
Subject: RE: Wanted Z80 In Circuit Emulator for Loan/Rent/Buy
Wow. Three Steve's with In Circuit Emulators, what are the odds on that.
Thank you for your offers of assistance.
I am trying to debug a random loss of program control. The problem is
repeatable but it takes many cycles for it to occur.
I believe I need an In-Circuit Emulator with good full speed trace
capabilities for a 4Mhz Z80. Something that would allow me to stop the
emulator at the point of the random error and then go backwards through the
code execution trace buffer to learn what occurred.
Could you let me know if your emulators offer such capabilities?
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