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ADDRESSING MODES
REGISTER ADDRESSING MODE (R)
In Register addressing mode (R), the operand value is the content of a specified register or register pair
(see Figure 3-1).
Working register addressing differs from Register addressing in that it uses a register pointer to specify an 8-byte
working register space in the register file and an 8-bit register within that space (see Figure 3-2).
8-bit Register
File Address
One-Operand
Sample Instruction:
DEC
4-bit
Working Register
Two-Operand
Instruction
(Example)
Sample Instruction:
ADD
3-2
Program Memory
OPCODE
Instruction
(Example)
CNTR
Figure 3-1. Register Addressing
Program Memory
dst
src
OPCODE
R1, R2
Figure 3-2. Working Register Addressing
dst
Point to One
Register in Register
File
Instruction Execution
;
Where CNTR is the label of an 8-bit register address
MSB Point to
RP0 ot RP1
3 LSBs
Point to the
Working Register
(1 of 8)
;
Where R1 and R2 are registers in the currently
selected working register area.
S3C8248/C8245/P8245/C8247/C8249/P8249
Register File
OPERAND
Value used in
Register File
RP0 or RP1
OPERAND
Selected
RP points
to start
of working
register
block
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