8086 instructions.pptx Instruction Sets in MPMC

8086 instructions

1. 8086 Instructions Classification of instruction set of 8086 Machine Control instructions Flag Manipulation instructions Shift & Rotate instructions String Instruction s. Presented by M.Deepak 23VV1A0438

2. Machine Control Instructions Used to control CPU operations. Examples: NOP – No Operation (used for timing) HLT – Halt processor until interrupt WAIT – Wait for external signal (TEST low) LOCK – Lock bus for atomic operation ESC – Escape to coprocessor No flags affected. Used for synchronization and system control.

3. Flag Manipulation Instructions Used to directly modify flag register. Examples: STC – Set Carry flag (CF=1) CLC – Clear Carry flag (CF=0) CMC – Complement Carry flag CLD – Clear Direction flag (string moves forward) STD – Set Direction flag (string moves backward) CLI – Disable Interrupts STI – Enable Interrupts PUSHF/POPF – Push/Pop Flags LAHF/SAHF – Load/Store AH with Flags

4. Shift & Rotate Instructions Used for bit-level operations. Shift Instructions: SHL/SAL – Shift Left (multiply by 2) SHR – Logical Shift Right SAR – Arithmetic Shift Right (preserves sign) Rotate Instructions: ROL/ROR – Rotate Left/Right RCL/RCR – Rotate through Carry flag Used in bit manipulation, encryption, and arithmetic logic.

5. String Instructions Operate on sequences of bytes or words. Examples: MOVS/MOVSB/MOVSW – Move String LODS/LODSB/LODSW – Load String STOS/STOSB/STOSW – Store String CMPS/CMPSB/CMPSW – Compare Strings SCAS/SCASB/SCASW – Scan String Prefixes: REP – Repeat CX times REPE/REPZ – Repeat while Equal REPNE/REPNZ – Repeat while Not Equal Direction Flag controls SI & DI increment/decrement.

6. Summary • Machine Control – Controls CPU state • Flag Manipulation – Sets/Clears processor flags • Shift & Rotate – Bit-level data processing • String Instructions – Operate on blocks of data These four groups help manage control flow, data, and processor behavior efficiently in 8086 programming.