Post by thread:[OT] Funny mnemonics = HCF

Russell Hedges wrote: > I got into this one late, but does anyone remember HCF? > Halt Catch Fire? From the 6502 days of yore. Yes, but as I remember, it applied to the 6800/6802. Whether it was deliberately copied into the 6502, I don't recall. -- Cheers, Paul B.

On Tue, 1 Feb 2000 22:54:25 +1100 "Paul B. Webster VK2BZC" <spam_OUTpaulbTakeThisOuTMIDCOAST.COM.AU> writes: > Russell Hedges wrote: > > > I got into this one late, but does anyone remember HCF? > > Halt Catch Fire? From the 6502 days of yore. > > Yes, but as I remember, it applied to the 6800/6802. Whether it > was > deliberately copied into the 6502, I don't recall. > -- > Cheers, > Paul B. I did a lot of 6800 stuff quite a while back, but don't recall HCF as an instruction. Could it have, instead, referred to a bit of the status register, the half-carry flag (carry from bit 3 to 4 used in the Decimal Adjust Accumulator instruction)? Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: dl.http://www.juno.com/get/tagj.

Harold M Hallikainen wrote: > I did a lot of 6800 stuff quite a while back, but don't recall HCF as > an instruction. Could it have, instead, referred to a bit of the > status register, the half-carry flag (carry from bit 3 to 4 used in > the Decimal Adjust Accumulator instruction)? Heh heh. No. It referred to the two undocumented instructions corresponding to opcodes $9D and $DD which were grudgingly referred to by Motorola as test instructions. These switched off all processing of opcodes until the next reset causing the processor to endlessly perform instruction fetches. Rather than a SLEEP instruction, these were DIE or ZOMBIE calls, however you chose to interpret it. Actually, they had their uses for - testing! Along with the other undocumented instructions (always a fun subject for microprocessors) such as NBA (AND B accumulator to A) and the various Store Immediate instructions (guess what they did?), these were documented in the article on page 85 of Byte Magazine, January 1978. Remember BYTE magazine? Used to discuss programming of computers, algorithmic development, hardware design and such. Those were the days! -- Cheers, Paul B.

> > I did a lot of 6800 stuff quite a while back, but don't recall HCF as an > instruction. Could it have, instead, referred to a bit of the status > register, the half-carry flag (carry from bit 3 to 4 used in the Decimal > Adjust Accumulator instruction)? Many years ago (late 70's) Gerry Wheeler exhaustively checked the execution of the undocumented opcodes in the 6800/6802 for a project we were working on. Two of the undocumented op codes ($D9 and $DD) caused the address bus to cycle continuously through a binary count and the instruction would never complete (HCF). Gerry wrote up the definition of the undocumented op-codes in an article in Byte. Walter Banks