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S3F84B8_UM_REV 1.00
6 INSTRUCTION SET
6-53
6.3.40 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 memory location is specified by a working register
pair. The contents of source location are loaded into the destination location, following which the
memory address is decremented. The contents of the source remain 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
:
Bytes Cycles
Opcode
(Hex)
Addr Mode
dst src
opc
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