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To: narses

I wish we knew what kind of chip it was. If it was a microprocessor, all modern high-complexity chips have “microcode” - basically, a cpu within a cpu - that allow instructions that are supposed to be executed in hardware (transistors, logic gates, etc) with a patch of instructions. Both AMD and Intel have routinely patched their chips with BIOS upgrades that first load any microcode revisions before starting up. It wouldn’t take much of a stretch to design “poisoned” microcode.

On the other hand, there was an illegal instruction (an unimplemented op code) on the Motorola 6800 that put the bus in an illegal state and locked the chip up so that it needed a power-on or hard reset - the infamous HCF (Halt and Catch Fire) instruction.


16 posted on 05/28/2012 8:24:19 PM PDT by The Antiyuppie ("When small men cast long shadows, then it is very late in the day.")
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To: The Antiyuppie
On the other hand, there was an illegal instruction (an unimplemented op code) on the Motorola 6800 that put the bus in an illegal state and locked the chip up so that it needed a power-on or hard reset - the infamous HCF (Halt and Catch Fire) instruction.

When it was discovered, some wag (don't recall who) gave the instruction that name. Some writers of assemblers included the HCF mnemonic.

They actually used that instruction during production line testing of each chip, because it exercised a goodly proportion of the logic.

But yeah, it would have been nice to have a trap for illegal instructions like that. At the time, they couldn't afford the random decode logic that it would have taken to implement the trap. No microcode on that chip, just pure random logic.

36 posted on 05/28/2012 10:17:20 PM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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