Intel mcs-48 manual Application Examples Byte Processing System, R1,A, 2sCOMPLEMENT and ADD

APPLICATION EXAMPLES

2 BYTE PROCESSING SYSTEM

A suggested model of a processing routine	(If Equal) Sets Flag and Exits
takes two single byte inputs from different	(If Not Equal) and Outputs the Larger to a
ports, compares them, and performs the	Third Port
following, depending on the result of the
comparison:
INPUT FIRST OPERAND
INPUT SECOND OPERAND
	NOT EQUAL

PROCESS: CLR	FO	;CLEAR FO BIT (INITIALIZE)
IN	A,P1	;READ FIRST INPUT, STORE IN RO
MOV	RO,A
IN	A,P2	;READ SECOND INPUT, STORE IN R1
MOV	R1,A
CPL	A	;SUBTRACT SECOND FROM FIRST
INC	A	;(2'sCOMPLEMENT AND ADD)
ADD	A,RO
JZ	EQUL	;BRANCH IF THEY ARE EQUAL
JNC	SECOND ;IF NEGATIVE, SECOND WAS LARGER
MOV	A,RO	;ELSE, OUTPUT FIRST
OUTL	BUS,A
JMP	DONE	;EXIT
SECOND: MOV	A,R1	;OUTPUT SECOND
OUTL	BUS,A
JMP	DONE	;EXIT
EQUL: CPL	FO	;SET FO
JMP	DONE	;EXIT

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