INSTRUCTION SET

S3C84E5/C84E9/P84E9

 

 

LDCD/LDED — Load Memory and Decrement

LDCD dst,src

LDED dst,src

Operation: dst src

rr rr – 1

These instructions are used for user stacks or block transfers of data from program or data memory to the register file. The address of the memory location is specified by a working register pair. The contents of the source location are loaded into the destination location. The memory address is then decremented. The contents of the source are unaffected.

LDCD refers to program memory and LDED refers to external data memory. The assembler makes "Irr" an even number for program memory and an odd number for data memory.

Flags: No flags are affected.

Format:

opc

dst src

 

 

Bytes

Cycles

Opcode

Addr Mode

 

 

(Hex)

dst

src

2

10

E2

r

Irr

Examples: Given: R6 = 10H, R7 = 33H, R8 = 12H, program memory location 1033H = 0CDH, and external data memory location 1033H = 0DDH:

LDCD

R8,@RR6

;

0CDH (contents of program memory location 1033H) is

 

 

 

loaded

 

 

; into R8 and RR6 is decremented by one;

 

 

;

R8 = 0CDH, R6 = 10H, R7 = 32H (RR6 RR6 – 1)

LDED

R8,@RR6

;

0DDH (contents of data memory location 1033H) is

 

 

 

loaded

 

 

; into R8 and RR6 is decremented by one

 

 

 

(RR6 RR6 – 1);

 

 

;

R8 = 0DDH, R6 = 10H, R7 = 32H

NOTE:LDED instruction can be used to read/write the data of 64-Kbyte data memory.

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Samsung S3C84E5 user manual LDCD/LDED Load Memory and Decrement, Ldcd dst,src Lded dst,src, Operation dst ← src