# micro operations in digital system

Typical Micro-operations
A. Register /Memory Reference
1. A <-- B B transferred to A 2. A<-- constant A constant transferred to A 3. AR<-- DR(ADR) Address portion of the DR transferred to the AR 4. IR<-- DR(OP) Op-code portion of the DR transferred to the Instruction Register 5. DR<-- M Contents of memory transferred to DR (i.e. read) 6. M<-- DR DR transferred to memory (i.e. write) B. Arithmetic 1. A<-- A + B Addition: content of A plus B transferred to A 2. A<-- A - B Subtraction: content of A minus B transferred to A 3. A<-- A + 1 Increment the content of A by one (count up) 4. A<-- A - 1 Decrement the content of A by one (count down) 5. A<-- A' 1's complement of the A register 6. A<-- A' + 1 2's complement of the A register 7. A<-- A + B' Content of A plus the 1's complement of B transferred into A 8. A<-- A + B' + 1 Content of A plus the 2's complement of B transferred into A C. Logic 1. F<-- 0 Clear 2. F<-- A & B AND 3. F<-- A & B' 4. F<-- A Transfer A {a.k.a. Pass A} 5. F<-- A' & B 6. F<-- B Transfer B {a.k.a. Pass B} 7. F<-- A ⊕ B Exclusive-OR 8. F<-- A | B OR 9. F<-- (A | B)' NOR 10. F<-- (A ⊕ B)' Exclusive-NOR 11. F<-- B' Complement B 12. F<-- A | B' 13. F<-- A' Complement A 14. F<-- A' | B 15. F<-- (A & B)' NAND 16. F<-- all 1's Set to all 1's Notes: (1) All logic operations are bit-wise operations, i.e. each bit in a given register is treated as a binary variable and the micro-operation is performed on the string of bits, without respect to adjacent bits. (2) The destination register chosen for logic operations is a register denoted by the letter F, but either A or B or any other register could be designated. (3) The symbols for AND, OR, and NOT are &, |, and an apostrophe (e.g. a'), respectively

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