1. REGISTER TRANSFER AND MICROOPERATIONS
• Register Transfer Language
• Register Transfer
• Bus and Memory Transfers
• Arithmetic Microoperations
• Logic Microoperations
• Shift Microoperations
• Arithmetic Logic Shift Unit

2. Register Transfer Language
MICROOPERATION
Digital systems are composed of modules that are constructed from digital components, such as registers, decoders, arithmetic elements, and control logic
MICROOPERATION: An elementary operation performed during
one clock pulse, on the information stored in one or more registers
ALU
(f)
Registers
(R)
1 clock cycle
operation ex.: shift, count, clear, load, add,...

3. REGISTER TRANSFER LANGUAGE
The internal hardware organization of a digital computer is best defined by specifying :
The set of registers it contains and their functions
The sequence of microoperations performed on the binary information stored
The control that initiates the sequence of microoperations
For any function of the computer, a sequence of
microoperations is used to describe it
----> Register transfer language
- A symbolic language
- A convenient tool for describing the
internal organization of digital computers
- Can also be used to facilitate the design
process of digital systems.

4. REGISTER TRANSFER Designation of a register - a register
- portion of a register
- a bit of a register
Common ways of drawing the block diagram of a register
Register
Showing individual bits R1 15 15 8 7 R2
PC(H)
PC(L)
Numbering of bits
Subfields
Representation of a transfer(parallel)
R2  R1
This statement implies that the hardware is available
The outputs of the source must have a path to the inputs of the destination
The destination register has a parallel load capability
Representation of a controlled(conditional) transfer
P: R2  R1
A binary condition(p=1) which determines when the transfer
is to occur
If (p=1) then (R2  R1)

5. HARDWARE IMPLEMENTATION OF CONTROLLED TRANSFERS
Register Transfer
HARDWARE IMPLEMENTATION OF CONTROLLED TRANSFERS
Implementation of controlled transfer
P: R2 R1
Block diagram
Control
Circuit P
Load R2
Clock n R1
Timing diagram t
t+1
Clock
Load
Transfer occurs here
A comma is used to separate two or more operations that are executed at the same time in one clock cycle

6. Questions
Show the block diagram of the hardware that implements the following register transfer statement:
yT2: R2R1, R1 R2
Explain the memory operation in each case.
A. R2M[AR]
B. M[AR]  R3

7. BUS AND MEMORY TRANSFER
Bus and Memory Transfers
BUS AND MEMORY TRANSFER
Bus is a path(of a group of wires) over which information is transferred,
from any of several sources to any of several destinations.
From a register to bus: BUS <- R
Register A
Register B
Register C
Register D
Bus lines
Bus lines
Load
Reg. R0
Reg. R1
Reg. R2
Reg. R3 D D 1 D 2 D 3 z
Select
E (enable)
2 x 4 w
Decoder

8. MEMORY TRANSFERS Memory read micro-op: DR  M ( DR  M[AR] )
Bus and Memory Transfers
MEMORY TRANSFERS
Memory
unit
Read AR
Write DR
Memory read micro-op: DR  M ( DR  M[AR] )
Memory write micro-op: M  DR ( M[AR]  DR )
Summary of Register Transfer Microoperations
A   B Transfer content of reg. B into reg. A
AR  DR(N) Transfer content of N bits portion of reg. DR into reg. AR
A  constant Transfer a binary constant into reg. A
ABUS  R1, Transfer content of R1 into bus A and, at the same time,
R2  ABUS transfer content of bus A into R2
AR Address register
DR Data register
M[AR] Memory word specified by reg. AR
DR  M[AR] Memory read operation: transfers content of
memory word specified by AR into DR
M[AR]  DR Memory write operation: transfers content of
DR into memory word specified by AR

9. ARITHMETIC MICROOPERATIONS
Four types of microoperations
- Register transfer microoperations
- Arithmetic microoperations
- Logic microoperations
- Shift microoperations
* Summary of Arithmetic Micro-Operations
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
R2  R2’+ 1 2's complement the contents of R2 (negate)
R3  R1 + R2’+ 1 subtraction
R1  R1 + 1 Increment
R1  R1 - 1 Decrement

10. BINARY ADDER Binary Adder
Arithmetic Microoperations
BINARY ADDER
Binary Adder
• The subtraction A-B can be carried out by the following steps:
Take the 1’s complement of B (invert each bit)
Get the 2’s complement by adding 1
Add the result to A
Binary Adder-Subtractor

11. Question
Draw the block diagram for the hardware that Implements the following statement:
x+yz: AR  AR + BR

12. Question

13. ARITHMETIC CIRCUIT Arithmetic Microoperations FA 4x1 MUX FA 4x1 MUX FA
Cin S1 S0 A0 X0 C0 S1 FA D0 S0 B0
4x1 Y0 C1 1
MUX 2 3 A1 X1 C1 S1 FA D1 S0 B1
4x1 Y1 C2 1
MUX 2 3 A2 X2 C2 S1 FA D2 S0 B2
4x1 Y2 C3 1
MUX 2 3 A3 X3 C3 S1 FA D3 S0 B3
4x1 Y3 C4 1
MUX 2 3
Cout 1

14. Question
The Arithmetic circuit in last slide has following values for S1, S0 and Cin. In each case determine the value of the output D in terms of the two input registers A and B. What is the corresponding microoperation?
S1 S0 Cin Output Microoperation
0 1 0

15. HARDWARE IMPLEMENTATION OF LOGIC MICROOPERATIONS
Question:
Draw the digital circuit that performs the following logical operations between reg. A and reg. B(draw the circuit for one bit), then list the circuit function table:
(AND, OR, XOR and Complement).

16. Answer Function table S1 S0 Output -operation 0 0 F = A  B ANDB i 1
4 X 1 F i
MUX 2 3
Select S 1 S
Function table
S1 S0
Output
-operation
F = A  B AND
F = AB OR
F = A  B XOR
F = A’ Complement

17. SHIFT MICROOPERATIONS
Shifts
- Logical shift : shift in a 0 into the extreme flip-flop
- Circular shift : circulates the bits of the register around the two ends
- Arithmetic shift : shifts a signed number (shift with sign extension)
Left shift -> multiplied by 2
Right shift -> divided by 2
Arithmetic shifts for signed binary numbers
- Arithmetic shift-right
Sign
bit
Rn-1
Rn-2 R1 R0
- Arithmetic shift-left Overflow V = Rn-1  Rn-2
Shift Micro-Operations
Symbol Description
R shl R Shift-left register R
R shr R Shift-right register R
R cil R Circular shift-left register R
R cir R Circular right-shift register R
R ashl R Arithmetic shift-left register R
R ashr R Arithmetic shift-right register R

18. Question
An 8-bits register R ahs the following value: , find the value of R after performing the following shifts:
Logical shift left
Logical shift right
Circular shift left
Circular shift right
Arithmetic shift left
Arithmetic shift right

19. Question

20. ARITHMETIC LOGIC SHIFT UNIT
Shift Microoperations
ARITHMETIC LOGIC SHIFT UNIT S3 S2 C i S1 S0
Arithmetic D i
Circuit
Select
4 x 1 C F
i+1 1
MUX i 2 3
Logic E i B i
Circuit A i
shr A
i-1 A
shl
i+1
S3 S2 S1 S0 Cin Operation Function
F = A Transfer A
F = A Increment A
F = A + B Addition
F = A + B Add with carry
F = A + B’ Subtract with borrow
F = A + B’ Subtraction
F = A Decrement A
F = A TransferA
X F = A  B AND
X F = A B OR
X F = A  B XOR
X F = A’ Complement A
X X X F = shr A Shift right A into F
X X X F = shl A Shift left A into F