[CCTECH] Interesting tidbit on 6502

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Fri Jun 7 11:33:55 2002

>From: "Ben Franchuk" <bfranchuk_at_jetnet.ab.ca>
>
>Loboyko Steve wrote:
>>
>> I'm building a 6800 machine right now and I was
>> wondering about this "Halt and Catch on Fire"
>> instruction. Is this for real. This is a serious
>> question. Is there actually an instruction that will
>> overheat the chip?
>
>Not on the 6800 but I believe some FORTH chips have that problem.
>This instruction for the 6800 if remember right just continually
>increments the address bus, ignoring any data read. Only a hard
>RESET will reset the machine from this state. I think the opcode
>is $00.
>

Hi
 Instructions that would continuously increment the address
are vary useful for debugging address decoding problems.
On an 8080, about the only useful sequence is to have
a pop and jmp, using 4 locations.
 It may have been that the 6800 one was a debug instruction
that was designed in.
Dwight
Received on Fri Jun 07 2002 - 11:33:55 BST