section 7 - Index of

CMP Compare CMPOperation:Assembler Syntax:S2 - S1 (parallel move) CMP S1, S2 (parallel move)Description: Subtract the source one operand, S1, from the source two accumulator,S2, and update the condition code register. The result of the subtraction operation is notstored.Note: This instruction subtracts 56-bit operands. When a word is specified as S1, it issign extended and zero filled to form a valid 56-bit operand. For the carry to be set correctlyas a result of the subtraction, S2 must be properly sign extended. S2 can beimproperly sign extended by writing A1 or B1 explicitly prior to executing the compare sothat A2 or B2, respectively, may not represent the correct sign extension. This note particularlyapplies to the case where it is extended to compare 24-bit operands such as XOwith A1.Example:CMP YO,B XO,X:(R6)+N6 Y1,Y:(RO)- ;comp. YO and B, save XO, Y1Before ExecutionAfter ExecutionB I $00:000020:000000 BI$00:000020:000000YO I $000024 YO I $000024SR I $0300 SR I $0319-Explanation of Example: Prior to execution, the 56-bit B accumulator contains thevalue $00:000020:000000 and the 24-bit YO register contains the value $000024. Theexecution of the CMP YO,B instruction automatically appends the 24-bit value in the YOregister with 24 LS zeros, sign extends the resulting 48-bit long word to 56 bits, subtractsthe result from the 56-bit B accumulator and updates the condition code register.