# 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