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fixed ORA_INDX and ORA_INDY

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jborza 2019-04-14 15:08:29 +02:00
parent 0d63342137
commit 6dfa71c5dc
2 changed files with 11 additions and 8 deletions
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1
.gitignore vendored
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@ -57,3 +57,4 @@ dkms.conf
/Release /Release
/emu6502.vcxproj.user /emu6502.vcxproj.user
/emu6502.vcxproj.filters /emu6502.vcxproj.filters
/data/.vscode/ipch

18
cpu.c
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@ -70,12 +70,12 @@ int emulate_6502_op(State6502 * state) {
break; //BRK break; //BRK
case NOP: break; //NOP case NOP: break; //NOP
case ORA_INDX: //ORA, indirect, x case ORA_INDX: //ORA, indirect, x
//The address to be accessed by an instruction using X register indexed absolute addressing is computed by taking the 16 bit address
//from the instruction and added the contents of the X register.
//For example if X contains $92 then an STA $2000,X instruction will store the accumulator at $2092 (e.g. $2000 + $92). (STA)
{ {
word address_indirect = pop_word(state) + state->x; //pre-indexed indirect
word address = read_word(state, address_indirect); //zero-page address is added to x register
byte indirect_address = pop_byte(state) + state->x;
//pointing to address of a word holding the address of the operand
word address = read_word(state, indirect_address);
ORA(state, state->memory[address]); ORA(state, state->memory[address]);
break; break;
} }
@ -87,10 +87,12 @@ int emulate_6502_op(State6502 * state) {
} }
case ORA_INDY: //ORA, indirect, y (post_indexed) case ORA_INDY: //ORA, indirect, y (post_indexed)
{ {
word address_indirect = pop_word(state); //post-indexed indirect
word address = read_word(state, address_indirect) + state->y; //zero-page address as an argument
byte indirect_address = pop_byte(state);
//the address and the following byte is read as a word, adding Y register
word address = read_word(state, indirect_address) + state->y;
ORA(state, state->memory[address]); ORA(state, state->memory[address]);
unimplemented_instruction(state);
break; break;
} }
case ORA_IMM: case ORA_IMM: