KS57C2308/P2308/C2316/P2316 SAM47 INSTRUCTION SET
5-91
XCHD — Exchange and Decrement
XCHD dst,src
Operation: Operand Operation Summary Bytes Cycles
A,@HL Exchange A and data memory contents; decrement
contents of register L and skip on borrow 12 + S
Description: The instruction XCHD exchanges the contents of the accumulator with the RAM location
addressed by register pair HL and then decrements the contents of register L. If the content of
register L is 0FH, the next instruction is skipped. The value of the carry flag is not affected.
Operand Binary Code Operation Notation
A,@HL 01111011A ↔ (HL), then L ← L–1;
skip if L = 0FH
Example: Register pair HL contains the address 20H and internal RAM location 20H contains the value
0FH:
LD HL,#20H
LD A,#0H
XCHD A,@HL ;A ← 0FH and L ← L – 1, (HL) ← "0"
JPS XXX ;Skipped since a borrow occurred
JPS YYY ;H ← 2H, L ← 0FH
YYY XCHD A,@HL ;(2FH) ← 0FH, A ← (2FH), L ← L – 1 = 0EH
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The “JPS YYY” instruction is executed since a skip occurs after the XCHD instruction.