I've read about some of the undocumented op codes. And yes, couldn't find = a use for any of them! ;-)=20 -- KF5QEO John Guillory westlakegeek@yahoo.com Cell: 601-754-9233 Pinger: 337-240-7890 Google Voice: 601-265-1307 On May 12, 2014, at 4:22 PM, IVP wrote: >> On the 80x86, there's another cool trick=20 >> Where it allows 3 different entry points to the same code...=20 >=20 > The 6510 has quite a few undocumented opcodes that the really > nerdy thought would bewilder casual users. For example there > were several that could be strung together in the middle of bona > fide-looking ML which looked like data (came up as ??? in a > disassembly) and looked nonsensical. But one function was to > actually operate as a computed branch and NOPs. So you > could appear to jump into the middle of a series of data bytes > without a crash, ending up in a common routine from one of > several entry points >=20 > Some opcodes were seemingly useless or innocuous, like one > that just did LDX $#0A, or LDY (X),Y. Some were NOPs, > like the official one, $#EA >=20 > Others were not so cool. There were no opcodes ending in 2 > (02, 12, ... F2). If you happened to execute an x2 byte the > processor/machine would just freeze and only a h/w reset could > get you out of it >=20 > Joe > --=20 > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .