The 6502 had a HCF (halt and catch fire) undocumented instruction.
I forget the opcode and if you knew what you were doing you could get the
instruction executed on the chip using any assembler.
Security through obscurity back in the 70s.
The chip was advanced enough that the DOD wanted to avoid it falling into the
“wrong” hands.
David
Sent from iPhone Hotblack Desiato
> On Oct 31, 2024, at 5:03 PM, Jon Elson via cctalk <cctalk@classiccmp.org>
> wrote:
>
> On 10/31/24 09:35, Donald Whittemore via cctalk wrote:
>> If I remember right I was told back in the early 70s by our IBM CE that
>> physical damage could be done to our model 30 or 40 if we ran a program that
>> did an Assembler instruction, B * For those non-Assembler people that is
>> an instruction to branch to the location of the instruction. I think it
>> might have caused a heat problem in the core or CCROS or TROS.
>>
>> Possible? Or is my 76 year old brain hallucinating?
>
> Hammering a single location in core could overheat the select wires, the
> individual cores or the select driver cards. I can believe this could
> happen. I seriously doubt it could harm the CCROS or TROS. The model 30 was
> SLOW, the original version (first 1000 machines) had a 2.5 us memory cycle
> time. But, a B instruction occupied 4 bytes. And the model 30 memory was
> ONE SINGLE BYTE wide! So, it would have to access 4 consecutive bytes over a
> 10 us period to read the entire instruction. This would involve t different
> select wires in one axis, but likely the same wire in the other axis.
>
> On the model 40, memory was 16 bits wide, so it would still have to access 2
> consecutive words.
>
> Anyway, I was told that on a model 40 (I think) that if you pressed and held
> stop, system reset, and load simultaneously, it would pop a component on a
> circuit card in the machine.
>
> Jon
