[CCTECH] Interesting tidbit on 6502

From: Jim Battle <frustum_at_pacbell.net>
Date: Fri Jun 7 10:21:30 2002

At 11:00 AM 6/7/02 -0400, you wrote:
> Why don't you learn that you don't always know what you're
> talking about?
>
> Indeed, the first step level of the 6800 had an undocumented
> opcode that
>results in 3 particular transistors turning on that connected Vcc to GND.
>The damage caused by these three transistors shorting damaged the silicon in
>the immediate area, rendering the CPU useless.


The R2000 MIPS CPU's had a similar problem. The TLB was implemented via a
small CAM. If more than one entry matched the virtual address, there was a
fight between two different words attempting to drive the output
bitlines. This wouldn't be a problem other than the fact that the TLB
contents were managed by software. Granted, the code would be supervisor
code and not user code, but when developing the supervisor software, there
was always the danger that buggy software could damage the chip.

I believe this was fixed in R3000 and later parts.



-----
Jim Battle == frustum_at_pacbell.net
Received on Fri Jun 07 2002 - 10:21:30 BST