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INSTRUCTION SET S3C84E5/C84E9/P84E9
6-56
LDCPD/LDEPD — Load Memory with Pre-Decrement
LDCPD dst,src
LDEPD dst,src
Operation: rr ← rr – 1
dst ← src
These instructions are used for 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 and is first
decremented. The contents of the source location are then loaded into the destination location. The
contents of the source are unaffected.
LDCPD refers to program memory and LDEPD refers to external data memory. The assembler
makes "Irr" an even number for program memory and an odd number for external data memory.
Flags: No flags are affected.
Format:
Bytes Cycles Opcode
(Hex)
Addr Mode
dst src
opc src | dst 2 14 F2 Irr r
Examples: Given: R0 = 77H, R6 = 30H, and R7 = 00H:
LDCPD @RR6,R0 ; (RR6 ← RR6 – 1)
; 77H (the contents of R0) is loaded into program memory
; location 2FFFH (3000H – 1H);
; R0 = 77H, R6 = 2FH, R7 = 0FFH
LDEPD @RR6,R0 ; (RR6 ← RR6 – 1)
; 77H (the contents of R0) is loaded into external data
memory
; location 2FFFH (3000H – 1H);
NOTE: LDEPD instruction can be used to read/write the data of 64-Kbyte data memory.