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Old 09-02-2009, 08:09 PM
rfeecs rfeecs is offline
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Default Emulator Status LEDs

I was playing with Rich Cini's Altair32 emulator and noticed that the status LEDs change when I single step. According to the theory of operations manual, the Altair stops and steps only at instruction fetch cycles. So the status LEDs should always be the same after a step, reflecting the status for an instruction fetch: MEMR is on, M1 is on, WO is on.

This video shows this behavior: http://www.youtube.com/watch?v=vAhp_LzvSWk

It looks like the emulator doesn't handle the status LEDs correctly.

Anyone with a working Altair care to confirm this?
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Old 09-03-2009, 04:37 PM
Geoff Harrison Geoff Harrison is offline
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Quote:
Originally Posted by rfeecs View Post
I was playing with Rich Cini's Altair32 emulator and noticed that the status LEDs change when I single step.
...
Anyone with a working Altair care to confirm this?
Yes, you're right. A real 8800 will step one full instruction at a time whereas Rich's emulator steps one byte at a time. There are a few differences (bugs?) in the emulator, but that doesn't detract from how useful it is for developing programs for the Altair.

Geoff.
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Old 09-03-2009, 05:55 PM
rfeecs rfeecs is offline
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That explains it.

Actually, from the point of view of understanding how the 8080 CPU works and looking at the status lines, stepping one machine cycle at a time is better.

I agree the emulator is a great tool. It's also great that he's collected so much of the original software ready to run on an Altair into one package.
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