RE: [Fwd: Diagnostic cartridges]

From: Marko Mäkelä (Marko.Makela_at_HUT.FI)
Date: 2002-01-29 11:23:39

On Tue, 29 Jan 2002, Nicolas Welte wrote:

> Recently I had some problems diagnosing RAM failures in two machines
> (one SX and one C64A breadbox), because my normal diagnostic ROM did
> not come up at all. I wonder if the KERNAL crashed because it relied
> on some RAM portions to be okay

The portions it relies to be okay are two bytes somewhere at $1f0-$1ff.

The RESET routine does just
LDX#xx:SEI:TXS:CLD:JSR$xxxx:...:RTS:BEQ/BNE$xxxx:JMP($8000) if the
CBM80 text is found at $8004-$8008.  The JSR'd routine checks the
text, and if the RAM is bad, the RTS at the end of this routine will
fail.  Stupid design by Commodore, I'd say.


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