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6502

What do < or > mean in LDA/STA command?

I understand the basics of the 6502 instruction set but have come across this code which is confusing me.

Can't find any reference to these in the 6502 manuals I have.

What do the < and > signify?

CLBASE  = $100
BPTR    = $25
ARM .BYT $1,$2  

LDA #<ARM
STA BPTR
LDA #>ARM
STA BPTR+1
LDA #>CLBASE
Solution

  • The prefix #< specifies the low byte of the operand, and #> specifies the high byte of the operand.

    E.g.

    LDA #>CLBASE ;This will be #$01
LDA #<CLBASE ;This will be #$00

    There's an assembler convention across the range of 6502-derived devices supported by most assemblers, such as ACME for instance. Here's the relevant section from WDC's W65C816S 8/16–bit Microprocessor datasheet.

    | Operand     | One Byte Result | Two Byte Result |
|-------------|-----------------|-----------------|
| #$01020304  | 04              | 0403            |
| #<$01020304 | 04              | 0403            |
| #>$01020304 | 03              | 0302            |
| #^$01020304 | 02              | 0201            |