1 Nov
2024
1 Nov
'24
2:27 a.m.
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(a)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