[CCTECH] Interesting tidbit on 6502

From: Tom Uban <uban_at_ubanproductions.com>
Date: Fri Jun 7 11:55:10 2002

I worked with a 6809 system back in the early 80s which
had an LED board to display the state of all of the system
signals. I don't recall the OP code, but there was one
which would continuously cycle the address, data, and
other signals until reset. It made the LEDs light up
like a christmas tree.

--tom

At 09:33 AM 6/7/02 -0700, you wrote:
>>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 - 11:55:10 BST