When making self modifying code or code that unrolls speed code, you have to know the value of the opcodes involved. To make this easier, all the opcodes have been given their own constant. The constant is found by writing the mnemonic in uppercase and appending the addressing mode. For example, the constant for a rts command is RTS and ‘lda #0’ is LDA_IMM. So, to place an rts command at target you write:
lda #RTS
sta target
You get the size of a mnemonic by using the asmCommandSize command
.var rtsSize = asmCommandSize(RTS) //rtsSize=1 .var ldaSize1 = asmCommandSize(LDA_IMM) //ldaSize1=2 .var ldaSize2 = asmCommandSize(LDA_ABS) //ldaSize2=3
Here are a list of the addressing modes and constant examples:
Table 14.1. Addressing Modes
| Argument | Description | Example constant | Example command |
|---|---|---|---|
| None | RTS | rts | |
| IMM | Immediate | LDA_IMM | lda #$30 |
| ZP | Zeropage | LDA_ZP | lda $30 |
| ZPX | Zeropage,x | LDA_ZPX | lda $30,x |
| ZPY | Zeropage,y | LDX_ZPY | ldx $30,y |
| IZPX | Indirect zeropage,x | LDA_IZPX | lda ($30,x) |
| IZPY | Indirect zeropage,y | LDA_IZPY | lda ($30),y |
| ABS | Absolute | LDA_ABS | lda $1000 |
| ABSX | Absolute,x | LDA_ABSX | lda $1000,x |
| ABSY | Absolute,y | LDA_ABSY | lda $1000,y |
| IND | Indirect | JMP_IND | jmp ($1000) |
| REL | Relative | BNE_REL | bne loop |
|
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