MOV R0,#42H
XCH A,R0
SWAP A
MOV R0,#42H ;(R0)=42 0010 1010
XCH A,R0;(A)<-->(R0)==>(A)=42即0010 1010
SWAP A ;A(D0-D3)<-->A(D4-D7)==>A为1010 0010即162
XCH A,R0;(A)<-->(R0)==>(R0)=162