NMOS 6510 Unintended Opcodes no more secrets (Christmas release, 24/12/14) (w) 2013-2014 groepaz/hitmen, all rights reversed Contents Preface...................................................................................................................................................I Scope of this Document....................................................................................................................I Intended Audience............................................................................................................................I What you get...................................................................................................................................II Naming Conventions.......................................................................................................................II Mnemonics.................................................................................................................................II Unintended Opcodes............................................................................................................................1 Overview..........................................................................................................................................1 Types................................................................................................................................................3 Combinations of two operations with the same addressing mode..............................................3 Combinations of an immediate and an implied command..........................................................3 Combinations of STA/STX/STY................................................................................................4 Combinations of STA/TXS and LDA/TSX................................................................................4 No effect......................................................................................................................................4 Lock-up.......................................................................................................................................4 stable Opcodes.................................................................................................................................5 SLO (ASO).................................................................................................................................5 Example:.................................................................................................................................6 RLA.............................................................................................................................................7 SRE (LSE)...................................................................................................................................8 Example: 8bit 1-of-8 counter.................................................................................................9 RRA..........................................................................................................................................10 SAX (AXS, AAX).....................................................................................................................11 Example: store values with mask.........................................................................................12 LAX..........................................................................................................................................13 Example: load A and X with same value..............................................................................14 DCP (DCM)..............................................................................................................................15 Example: decrementing loop counter...................................................................................16 Example: decrementing 16bit counter..................................................................................16 ISC (ISB, INS)..........................................................................................................................17 Example: incrementing loop counter...................................................................................18 Example:...............................................................................................................................18 ANC..........................................................................................................................................19 Example: implicit enforcement of carry flag state...............................................................20 Example: remembering a bit................................................................................................20 ALR (ASR)...............................................................................................................................21 Example:...............................................................................................................................21 Example: fetch 2 bits from a byte........................................................................................22 Example:...............................................................................................................................22 ARR..........................................................................................................................................23 Example: rotating 16 bit values............................................................................................24 Example:...............................................................................................................................25 Example: shift zeros or ones into accumulator....................................................................25 SBX (AXS, SAX).....................................................................................................................26 Example: decrement X by more than 1................................................................................27 Example: decrement nibbles................................................................................................28 Example: apply a mask to an index......................................................................................29 SBC (USBC).............................................................................................................................30 LAS (LAR)...............................................................................................................................30 Contents NOP...........................................................................................................................................31 NOP (DOP, SKB)......................................................................................................................31 NOP (TOP, SKW).....................................................................................................................32 Example: acknowledge IRQ ................................................................................................33 JAM (KIL, HLT).......................................................................................................................34 Example: stop execution .....................................................................................................34 unstable Opcodes...........................................................................................................................35 'unstable address high byte' group.............................................................................................35 SHA (AXA, AHX)...............................................................................................................36 Example: SAX abs, y.......................................................................................................37 Example: SAX (zp), y......................................................................................................37 SHX (A11, SXA, XAS)........................................................................................................38 Example: STX abs, y.......................................................................................................39 SHY (A11, SYA, SAY).........................................................................................................40 Example: STY abs, x.......................................................................................................41 TAS (XAS, SHS)..................................................................................................................42 'Magic Constant' group.............................................................................................................43 ANE (XAA).........................................................................................................................43 Example: clear A..............................................................................................................44 Example: read the 'magic constant'..................................................................................44 LAX #imm (ATX, LXA, OAL)............................................................................................45 Example: clear A and X...................................................................................................46 Example: read the 'magic constant'..................................................................................46