Addressing modes

Immediate

The data follows the opcode.

 lda     #3      * A=4
 adda    #2      * A=6 (A+=2)

Direct

Also called base page or base page direct addressing. It combines the DP register with the single byte operand.

DP=0

 lda     $0      * DIRECT because the address 0 is withing the DP
 lda     <$1234  * DIRECT forces assembler to use direct. Loads A with data at $1234.

Indexed

Store or load from a memory location pointed to by X,Y,U,S.

tiledata        fcb     $fd
                ldx     #tiledata       * IMMEDIATE X points to tiledata
                lda     ,x              * INDEXED A=$FD, loaded from the address X points to

Extended

Loading a register from memory and storing a register to memory. The operand value is the address. Note that if the address is within the DP, it will become direct.

tiledata fcb $fd
         lda tiledata  * EXTENDED A=$FD
         lda $3000     * EXTENDED loads whatever was in memory $3000
         sta $FFD9     * EXTENDED stores A to address FFD9
         inc $3000     * if the byte at $3000 = 1 it would now be 2
         inc >$3000    * forces the assembler to use extended

Inherent

The instruction doesn't nave an operand.

 inca