The original fake6502.c has been split up into subcomponents, rather than being one long file - support functions, 6502 instructions, address modes, data tables and 65c02 extensions.

The file tables.h is now created from 6502.opcodes and 65c02.opcodes which are lists of instructions, cycle times, address modes and opcodes.

The python script buildtables.py creates this.

Minor changes have been made to modes.h and instructions.h to correct for 65C02 behaviour. These are documented in the files.

Breaking Changes

Note: these breaking changes are only in the emulator. The behaviour is correct for a 65C02, which is almost but not the same as a 6502.

(1) BRK clears D after pushing on the stack. Probably unimportant as most routines in 6502 code CLD to get round this issue anyway.

(2) ADC/SBC In Decimal Mode, these now set N and Z flags. They did not previously. It is possible that code may rely on this to preserve flag status through an ALU operation but unlikely.

(3) JMP The absolute indirect mode JMP (xxxx) had a bug where JMP ($12FF) got its target address from $12FF and $1200. This bug is corrected. This could break code with oddly positioned jump tables. Even align any vector tables or memory vectors.

(4) (Misc) Undocumented instructions now do not work. They don't work on a 65C02.

Also note that read-modify-write instructions all now do not do the double write. ASL xx would do read xx ; write xx ; write shifted xx on a 6502. On a 65C02 it does not. However, the emulator did not emulate this behaviour anyway, so it doesn't actually matter.

Paul Robson 4/Sep/19

Testing

Fixed stz bug .... writing a ... duh !