1 Nov
2024
1 Nov
'24
12:37 p.m.
I had remembered the HCF as being a z-80 thing, so I searched for it.
All I can find says it was 6800, not 6502.
https://en.wikipedia.org/wiki/Halt_and_Catch_Fire_(computing)
http://www.ffd2.com/fridge/docs/6502-NMOS.extra.opcodes
http://www.z80.info/zip/z80-documented.pdf
New question: what do emulators do with these undocumented instructions? I seem to recall
in the 8086 (?) family tree, some clone cpu chips had actually useful instructions.
<pre>--Carey</pre>
On 11/01/2024 11:55 AM CDT Peter Coghlan via cctalk
<cctalk(a)classiccmp.org> wrote:
David Barto wrote:
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
Did someone tell you this on April 1st?
Regards,
Peter Coghlan
Sent from my DEC Alphaserver 800