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@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
