joeloda@aicchi.UUCP (Joseph D. Loda) (03/21/85)
Well, I knew if I waited long enough, it was bound to surface! The April 1985 issue of InCider magazine contains a list of undocumented 6502 op codes. The article is located in the Apple Clinic column of the magazine. These op codes are for the Synertek 6502; they may not be applicable to other manufacturers chips. Note that when you pick this up, instruction $12 does not cause the HCF (halt and catch fire) operation. This, and many other undocumented functions $?2 range are described as "a five cycle instruction which ends with the processor hung at $FFFF; the 6502 must be reset to escape this condition". For that matter, stick your fingers (after grounding) to any of the chips in your Apple after it has been running awhile. They'll probably be rather hot. The HCF is an old "funny op code" from a list of these that was old when I first saw it (> 7 years ago). If anyone wants a list of these, mail me; if enough response, I'll post my list of silly op codes. Surely you didn't beleive that some software instruction would set a chip on fire ??? :-) -- Joe Loda Analysts International (Chicago Branch) (312) 882-4673 ..!ihnp4!aicchi!joeloda