Wanted Z80 In Circuit Emulator for Loan/Rent/Buy

[Randy Dawson]

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.

Randy

> Date: Sat, 21 Feb 2009 21:02:24 -0500
> From: robo58 at optonline.net
> To: cctech at classiccmp.org
> CC: 
> 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?
> 
> Thanks Robo
> 

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