The document discusses processor logic design and register transfer logic. It describes registers, their functions, and how data is transferred between registers. There are four categories of microoperations - interregister transfer, arithmetic, logic, and shift. Interregister transfer moves data between registers without changing it. Arithmetic operations perform math on register data. Logic operations perform AND, OR, etc on register bit values. Shift operations serially move data within a register. The document also discusses conditional control statements that allow different microoperations to be selected based on register values.

1. MODULE-V
Part-I
Processor Logic Design
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2.  Contents
• Register Transfer Logic
 Inter Register Transfer
 Arithmetic Microoperations
 Logic Microoperations
 Shift Microoperations
• Conditional Control Statements
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3. 3
Registers
 Register
• a collection of binary storage elements
• included a set of flip-flop
• n-bit register store n-bit binary information
 Frequently used to perform simple data
storage and data movement and processing
operations

4. 4
Register and Load Enable
Register with load enable
by clock gating

5. 5
Register transfer
 Large digital systems are often designed by modular,
hierarchical approach
 Large digital systems are partitioned into two types of modules
• Data path: performs data-processing operations
• Control unit: determine the sequence of those operations

6. 6
Register transfer
 The registers are assumed to be basic components of the
digital system
 Register transfer operation: movement on the data stored
in register and the processing performed on the data
 The basic components for describing a digital system in
register transfer logic is:
• The set of registers in digital systems and their
functions.
• The operations performed on the data
• Control on the sequence of operations

7. Register transfer Operations
 Microoperations: operations executed on data stored in one
or more registers.
 For any function of the computer, a sequence of
micro operations is used to describe it
 The result of the operation may be:
• replace the previous binary information of a register or
• transferred to another register
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8. Register Transfer Language
 Register Transfer Language (RTL) : a symbolic notation to
describe the microoperation transfers among registers
Next steps:
• Define symbols for various types of microoperations,
• Describe the hardware that implements these
microoperations
 A statement in a register transfer language consists of a
control function and a list of micro operations.
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9.  The type of microoperations in digital systems can be
classified into four categories:
• Interregister –transfer microoperations do not change the
information content when the binary information moves from one
register to another.
• Arithmetic micro operations perform arithmetic on numbers stored
in registers.
• Logic microoperations perform operations such as AND and OR on
individual pairs of bits stored in registers.
• Shift microopeartions specify operations for shift registers.
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10. 10
InterRegister Transfer
 Computer registers are designated by capital letters
(sometimes followed by numerals) to denote the function
of the register
 R1: processor register
 MAR: Memory Address Register (holds an address
for a memory unit)
 PC: Program Counter
 IR: Instruction Register
 SR: Status Register

11.  The individual flip-flops in an n-bit register are numbered
in sequence from 0 to n-1 (from the right position toward
the left position)
11
R1
Register R1
7 6 5 4 3 2 1 0
Showing individual bits
A block diagram of a register

12. 12
PC
Numberingof bits
Partitioned intotwoparts
15 0
PC(H)
PC(L)
07815
LowerbyteUpperbyte
Other ways of drawing the block diagram of a register:

13. 13
 Information transfer from one register to another is described
by a replacement operator: R2 ← R1
 This statement denotes a transfer of the content of register R1
into register R2
 The transfer happens in one clock cycle
 The content of the R1 (source) does not change
 The content of the R2 (destination) will be lost and replaced by
the new data transferred from R1
 We are assuming that the circuits are available from the outputs
of the source register to the inputs of the destination register,
and that the destination register has a parallel load capability

14. 14
 The condition which determines when the transfer is to occur
is called a control function.
 Conditional transfer occurs only under a control condition
 Representation of a (conditional) transfer
P: R2 ← R1
 A binary condition (P equals to 0 or 1) determines when the
transfer occurs
 The content of R1 is transferred into R2 only if P is 1

15. 15

16.  The control function is included with the statement is as
follows:
x’T1: A ← B
 The control function is terminated with a colon.
 It shows that the transfer operation be executed by the
hardware only when the Boolean function x’T1 = 1
• i.e,when variable x=0 and timing variable T1 = 1
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17. Hardware implementation for the
above statement is as follows
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18. 18
7-3 Register Transfer Operations
More register transfer operation executed at the same time:
K3: R2 ←R1, R1 ←R2

19.  Consider the two statements:
 T1: C ← A
 T5: C ← B
• Destination register receives information from two
sources, but not at the same time.
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20. 20

21. Bus and Memory Transfers
 Paths must be provided to transfer information from one register
to another
 A Common Bus System is a scheme for transferring information
between registers in a multiple-register configuration
 A bus: set of common lines, one for each bit of a register,
through which binary information is transferred one at a time
 Control signals determine which register is selected by the bus
during each particular register transfer
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22. 22

23. 23

24. 24

25. Memory Transfer
 Memory read : Transfer from memory
 Memory write : Transfer to memory
 Data being read or wrote is called a memory word (called
M)
 It is necessary to specify the address of M when writing
/reading memory
 This is done by enclosing the address in square brackets
following the letter M
 Example: M[0016] : the memory contents at address
0x0016
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26. 26

27.  Assume that the address of a memory unit is
stored in a register called the Address
Register AR
 Lets represent a Data Register with DR,
then:
 Read: DR ← M[AR]
 Write: M[AR] ← DR
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28. Memory Transfer
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29.  The transfer of information from a bus into one of many
destination registers is done:
• By connecting the bus lines to the inputs of all
destination registers and then:
• activating the load control of the particular destination
register selected
 We write: R2 ← C to symbolize that the content of register
C is loaded into the register R2 using the common system
bus
 It is equivalent to: BUS ←C, (select C)
R2 ←BUS (Load R2)
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30. 30

31. Arithmetic Microoperations
 The basic arithmetic microoperations are: addition,
subtraction, increment, decrement, and shift
 Addition Microoperation:
R3 ←R1+R2
 Subtraction Microoperation:
R3 ←R1-R2 or :
R3 ←R1+R2+1
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32.  One’s Complement Microoperation:
R2 ←R2
 Two’s Complement Microoperation:
R2 ←R2+1
 Increment Microoperation:
R2 ←R2+1
 Decrement Microoperation:
R2 ←R2-1
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33. 33

34. 34

35. Logic microoperations
 Logic microoperations specify binary operations for a
string of bits stored in registers.
 These operations consider each bit in the registers
seperately and treat it as a binary variable.
 Exclusive –OR operation symbolized by the statement:
F ← A ⊕ B
 If the contents of register A is 1010 and B is 1100, the
information transferred to register F is 0110:
 1010 content of A
 1100 content of B
 0110 content of F ← A ⊕ B
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36.  16 different possible logic operations that
can be performed with two binary variables,
 The symbol ∨ will be used to denote OR
microoperation and the symbol ∧ to denote
an AND microoperation.
 Complement microoperation is the sameas
1’s complement and use a bar on top of the
letter that denotes the register.
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37. Logic microoperations
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38. Shift Microoperations
 Used for serial transfer of data
 Also used in conjunction with arithmetic, logic, and other
data-processing operations
 The contents of the register can be shifted to the left or to
the right
 As being shifted, the first flip-flop receives its binary
information from the serial input
 Three types of shift: Logical, Circular, and Arithmetic
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41. 41

42. 42

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45. 45

46. CONDITIONAL CONTROL STATEMENTS
 Conditional control statement is symbolized by an if-then –
else statement as follows:
 P: If (condition) then [microoperation(s)] else
[microoperation(s)]
• It means that if the control condition stated within the
parentheses after the word if is true, then the
microoperation enclosed within the parentheses after
the word then is executed.
• If the condition is not true, the microoperation listed
after the word else is executed.
• In any case the control function P must occur for
anything to be done.
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47.  Eg:
 T2: If(C=0) then (F ← 1) else (F ← 0)
 F is assumed to be a 1-bit register(flip-flop) that can be set
or cleared.
 If register C is a 1-bit register, the statement is equivalent
to the following two statements:
C’T2: F ←1
CT2: F ←0
• Only one of the microoperation will be executed during T2,
depending on the value of C
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