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coding the addressing modes

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This commit is contained in:
Thiago Auler 2017-11-13 17:39:10 -02:00
parent 2cb3f865a8
commit 4ced079268
3 changed files with 45 additions and 21 deletions
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2
src/6502.c
View File

@ -100,7 +100,6 @@ void execute()
case TXA: return txa();
case TXS: return txs();
case TYA: return tya();
case XXX: return xxx();
}
switch (opcode_in_table)
@ -128,7 +127,6 @@ void execute()
case STA: return sta();
case STX: return stx();
case STY: return sty();
case XXX: return xxx();
}
}

1
src/inc/opcodes.h
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@ -53,7 +53,6 @@ typedef enum address_mode am;
am address_mode;
void xxx(); // invalid opcode
void adc(); // add memory to accumalator with carry
void and(); // and memory with accumulator
void asl(); // shift left one bit (memory on accumulator)

63
src/opcodes.c
View File

@ -1,43 +1,70 @@
#include "inc/opcodes.h"
#include "inc/memory.h"
db fetch_operand()
{
db operand;
dw address;
db operand;
void fetch_operand()
{
switch (address_mode)
{
case immediate:
operand = read_byte(pc);
address = pc;
operand = read_byte(address);
pc = pc + 1;
break;
case zero_page:
operand = read_byte(pc);
operand = read_byte(operand);
address = read_byte(pc);
operand = read_byte(address);
pc = pc + 1;
break;
case zero_page_x:
operand = read_byte(pc);
operand = read_byte(operand + x);
address = read_byte(pc);
address = address + x;
operand = read_byte(address);
pc = pc + 1;
break;
case zero_page_y:
operand = read_byte(pc);
operand = read_byte(operand + y);
address = read_byte(pc);
address = address + y;
operand = read_byte(address);
pc = pc + 1;
break;
case accumulator:
address = pc;
operand = ac;
break;
case absolute:
address = read_word(pc)
operand = read_byte(address);
pc = pc + 2;
case absolute_x:
address = read_word(pc);
address = address + x;
operand = read_byte(address);
pc = pc + 2;
break;
case absolute_y:
address = read_word(pc);
address = address + y;
operand = read_byte(address);
pc = pc + 2;
break;
case indirect_x:
address = read_byte(pc);
address = address + x;
address = read_word(address);
operand = read_byte(address);
pc = pc + 1;
break;
case indirect_y:
address = read_byte(pc);
address = read_word(address);
address = address + y;
operand = read_byte(address);
pc = pc + 1;
break;
}
return operand;
}
void xxx()
{
// invalid opcode
return nop();
}
void adc()