
HD404339 Series
14
Addressing Modes
RAM Addressing Modes
Register Indirect Addressing Mode:
The contents of the W, X, and Y registers (10 bits total) are used as
a RAM address.
Direct Addressing Mode:
A direct addressing instruction consists of two words. The first word contains
the opcode, and the contents of the second word (10 bits) are used as a RAM address.
Memory Register Addressing Mode (LAMR, XMRA):
The memory registers (MR), which are located
in 16 addresses from $040 to $04F, are accessed with the LAMR and XMRA instructions.
0
0
9
9
Opcode
Register Indirect Addressing
2nd instruction
word
RAM address
Direct Addressing
Instruction
9
0
0
9
RAM address
1st instruction
word
3
7
3
0
Memory Register Addressing
0
9
RAM address 0 0 0 1 0 0
Opcode
Instruction
3
0 3
0
0
1
W
X
Y
Figure 7 RAM Addressing Modes