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Module 3: Instruction Set and Programming

20202m

Which among the single operand instructions complements the accumulator without affecting any of the flags?
(i) CLR
(ii) SETB
(iii) CPL
(iv) All of the above

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Answer: (iii) CPL

Explanation: CPL A (Complement Accumulator) does A = ~A (ones complement) and affects no flags. CLR A clears A to 0 and also no flags but not complement. SETB sets a bit flag. Complement operations in 8051 (CPL A, CPL C, CPL bit) are defined to leave PSW flags unchanged (except CPL C complements Carry). For single-operand complement of accumulator without flag change, CPL A is correct.

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