ADDRESSING MODES

S3C84E5/C84E9/P84E9

 

 

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).

 

Program Memory

8-bit Register

 

File Address

dst

 

 

OPCODE

One-Operand

 

Instruction

 

(Example)

 

Register File

OPERAND Point to One

Register in Register

File

Value used in

Instruction Execution

Sample Instruction:

DEC CNTR

; Where CNTR is the label of an 8-bit register address

Figure 3-1. Register Addressing

 

Program Memory

4-bit

 

 

 

 

Working Register

 

 

dst

src

 

 

 

 

 

OPCODE

Two-Operand

 

 

Instruction

 

 

(Example)

 

 

MSB Point to

RP0 ot RP1

3 LSBs

Point to the Working Register (1 of 8)

Register File

RP0 or RP1

OPERAND

Selected RP points to start of working register block

Sample Instruction:

 

ADD

R1, R2

; Where R1 and R2 are registers in the currently

 

 

selected working register area.

Figure 3-2. Working Register Addressing

3-2

Page 57
Image 57
Samsung S3C84E5 user manual Register Addressing Mode R, Opcode, DEC Cntr, Operand