ACME ...the ACME Crossassembler for Multiple Environments --- Undocumented ("illegal") opcodes --- In release 0.87, support for some of the undocumented opcodes of the 6502 processor was added. In release 0.89, some more were added. In release 0.94.8, another one was added (lxa). In release 0.95.3, C64DTV2 support was added, which includes these opcodes as well. Here are the mnemonics, addressing modes and generated opcodes: | addressing mode | Mnemo | 8 8,x 8,y 16 16,x 16,y (8,x) (8),y | performs: ------+--------------------------------------------------+----------- slo | 07 17 -- 0f 1f 1b 03 13 | asl + ora rla | 27 37 -- 2f 3f 3b 23 33 | rol + and sre | 47 57 -- 4f 5f 5b 43 53 | lsr + eor rra | 67 77 -- 6f 7f 7b 63 73 | ror + adc sax | 87 -- 97 8f -- -- 83 -- | stx + sta lax | a7 -- b7 af -- bf a3 b3 | ldx + lda dcp | c7 d7 -- cf df db c3 d3 | dec + cmp isc | e7 f7 -- ef ff fb e3 f3 | inc + sbc | addressing mode | Mnemo | implied #8 8 8,x 16 16,x | performs: ------+-------------------------------------+------------------------ anc | -- 0b* -- -- -- -- | A = A & arg, then C=N asr | -- 4b -- -- -- -- | A = A & arg, then lsr arr | -- 6b -- -- -- -- | A = A & arg, then ror sbx | -- cb -- -- -- -- | X = (A & X) - arg dop | 80** 80 04 14 -- -- | skips next byte top | 0c** -- -- -- 0c 1c | skips next two bytes jam | 02 -- -- -- -- -- | crash (wait for reset) lxa | -- ab*** -- -- -- -- | A/X = (A | ??) & arg Example: !cpu 6510 ; activate additional mnemonics... lax (some_zp_label,x) ; ...and use them. No, this dcp (other_zp_label),y ; example does not make sense. *) Up until ACME version 0.95.1, anc#8 generated opcode 0x2b. Since ACME version 0.95.2, anc#8 generates opcode 0x0b. Both opcodes work the same way on a 6510. I am told 0x2b does not work on the C64DTV2. **) Note that "dop" and "top" can be used with implied addressing, but the generated opcodes are those for immediate and 16-bit absolute addressing, respectively. Using dop/top with x-indexed addressing might have its uses when timing is critical (crossing a page border adds a penalty cycle). ***) This opcode is said to first perform an ORA with an arbitrary(!) value, then do an AND with the given argument, then do a TAX. This means it is unstable and therefore useless - unless the given argument is zero, in which case it reliably clears both A and X. There is no guarantee that these opcodes actually work on a given 6502 (or 6510, or 8500, or 8502) CPU. But as far as I know, nobody ever found an unmodified C64/C128 where these illegals didn't work. That's why I used "6510" as the CPU keyword instead of "6502illegal" or something like that. These illegals will definitely *not* work on 65c02 and 65816 CPUs. But I really should not have to tell you that ;) Because there are no official mnemonics for these opcodes, different people use different names for them. I hope my choices are not too exotic for your taste. Just for the sake of completeness: Here are all the remaining opcodes (the ones ACME won't generate even with "6510" cpu): Opcode| Description C64DTV2 ------+-------------------------------------------------------------- 12 | same as 02 and others jam CRASH bra rel 1a | same as (*legal*) ea nop 22 | same as 02 and others jam CRASH 2b | same as 0b anc #8 dop 32 | same as 02 and others jam CRASH sac #8 34 | same as 14 and others dop 8,x 3a | same as (*legal*) ea nop 3c | same as 1c and others top 16,x 42 | same as 02 and others jam CRASH sir #8 44 | same as 04 dop 8 52 | same as 02 and others jam CRASH 54 | same as 14 and others dop 8,x 5a | same as (*legal*) ea nop 5c | same as 1c and others top 16,x 62 | same as 02 and others jam CRASH 64 | same as 04 dop 8 72 | same as 02 and others jam CRASH 74 | same as 14 and others dop 8,x 7a | same as (*legal*) ea nop 7c | same as 1c and others top 16,x 82 | same as c2/e2 dop #8, but said to CRASH sometimes 89 | same as 80 dop #8 8b | see notes below 92 | same as 02 and others jam CRASH 93 | see notes below 9b | see notes below 9c | see notes below 9e | see notes below 9f | see notes below b2 | same as 02 and others jam CRASH bb | see notes below c2 | same as 82/e2 dop #8, but said to CRASH sometimes d2 | same as 02 and others jam CRASH d4 | same as 14 and others dop 8,x da | same as (*legal*) ea nop dc | same as 1c and others top 16,x e2 | same as 82/c2 dop #8, but said to CRASH sometimes eb | same as (*legal*) e9 sbc #8 f2 | same as 02 and others jam CRASH f4 | same as 14 and others dop 8,x fa | same as (*legal*) ea nop fc | same as 1c and others top 16,x Concerning opcodes 8b, 93, 9b, 9c, 9e, 9f, bb: These opcodes are said to be unstable. For more information about what they do, see these documents: John West, Marko Mäkelä. '64doc' file, 1994/06/03. Extra Instructions Of The 65XX Series CPU, Adam Vardy, 27 Sept. 1996 6502 Undocumented Opcodes, by Freddy Offenga, 5/17/1997 AAY64 (All About Your 64) I did not see much point in assigning mnemonics for these opcodes. The reference documents above call them: 8b: ane, xaa 93: sha, axa, ahx 9b: shs, tas, xas 9c: shy, say, sya 9e: shx, xas, sxa 9f: sha, axa, ahx bb: las, lar, lae