Chapter 4 Register Transfer and Microoperations . Dr. Bernard Chen Ph.D. University of Central Arkansas Spring 2009. Outline. Bus Transfer Memory Transfer Microoperations. This Chapter contains. A basic computer: 1. The set of registers and their functions;
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Dr. Bernard Chen Ph.D.
University of Central Arkansas
Data can move from register to register.
Digital logic used to process data
C A + B
Use of Multiplexers to Select between Two Registers
Used for lowest bit
Used for highest bit from each register
Normal input A
If C=1, Output Y = A
If C=0, Output = High-impedance
Control input C
Read: DR M[AR]
Write: M[AR] R1
Symbolic designation Description
R3 ← R1 + R2 Contents of R1 plus R2 transferred to R3 R3 ← R1 – R2 Contents of R1 minus R2 transferred to R3 R2 ← R2 Complement the contents of R2 (1’s complement) R2 ← R2 + 1 2’s Complement the contents of R2 (negate) R3 ← R1 + R2 + 1 R1 plus the 2’s complement of R2 (subtract) R1 ← R1 + 1 Increment the contents of R1 by one R1 ← R1 – 1 Decrement the contents of R1 by oneArithmetic Microoperations
• The addition and subtraction operations cane be combined into one common circuit by including an exclusive-OR gate with each full-adder.
0 0 0
0 1 1
1 0 1
1 1 0
B3 B2 B1 B0 1
Always added to 1
S3 S2 S1 S0