Samsung 8-Bit CMOS Microcontroller, S3C9228/P9228 user manual LDCD/LDED Load Memory and Decrement

S3C9228/P9228 SAM88RCRI INSTRUCTION SET

LDCD/LDED — Load Memory and Decrement

LDCD/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 references program memory and LDED references 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

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