This document discusses register transfer language and micro-operations. It describes how registers store information and how register transfer language is used to define the transfer of data between registers using micro-operations like shift, clear and load. It also discusses how bus systems, memory transfers, and arithmetic logic shift units are used to perform these micro-operations and transfer data.

1. Register Transfer and Micro-
Operation
Register and Register Transfer Language
Bus and Memory Transfer
Arithmetic, Logic and Shift μ-operation
Arithmetic Logic Shift Unit

2. Register
 Group of flip-flops capable of storing one bit of
information.
 They may have combinational gates to perform
certain data processing.
 Are at the top of memory hierarchy and provide
fastest way of data access.

3. Register Transfer Language
 Digital System is interconnection of modules.
 Modules are constructed using digital components
and interconnected using common data and control
paths.
 They are best defined by the operation they perform
on the stored data(μ-operation).
 Example of μ-operations are shift, clear , load etc.

4.  The internal hardware of the computer is best
defined by specifying:
 Set of register it contains and their functions
 μ-operations that can be performed on the stored binary data
 Control that initiates the sequence of μ-operation.
 It is possible to specify the μ-operations in words but
that will be lengthy.
 Special symbolic notation is used to describe the μ-
operation among the register called Register
Transfer Language(RTL).

5. Register Transfer
 Computer registers are denoted by capital
letters(sometimes followed by numerals) to denote
the function of the register.
 Examples:
 MAR: Memory Address Register
 PC: Program Counter
 R1: Processor Register

7.  Information transfer from one register to another is
designated as: R2 R1.
 Normally we want the transfer to occur under a
predetermined condition as
 If(P=1) then (R2 R1. )
 P is the control signal. Generally control function in
included in the statement as follows:
 P: R2 R1
 Every statement in RTL need hardware for above
RTL hardware will be as:

10. Bus and Memory Transfers
 Digital computer have many registers and paths
must be provided to transfer information.
 No. of wires will be excessive if we connect each
register with the other one.
 A more efficient scheme for transferring information
in multiple register system is by the use of the
common bus system.
 Control signals are used to select the register.

11.  One way of constructing a common bus system is by
the use of multiplexer.
 Figure below show the 4 register common bus
system.
 It consist of Multiplexer and selection lines

14.  In general, a bus system will multiplex k registers of
n bits each to produce an n-line common bus.
 Common bus for 8 registers of 16 bits requires, 16
multiplexer having 8 data input lines.
 The transfer of information from bus to one of many
register can be accomplished by connecting bus lines
to the inputs of all register and activating the load
signal of required one.

15.  If we need to transfer the content of register C to
register R1, it can be represented as:
 It is convenient to show the direct transfer as:

16. Three State Bus Buffer
 A bus system can also be constructed using three
state gate.
 Three state gate has 3 outputs one low and other
high as like other gates.
 The third output is the high impedance state which
behave like the open circuit and does not have any
logic significance.
 The most commonly used gate in bus design is the is
3 state buffer gate.

19. Memory Transfer
 Transfer of information from memory word to
outside environment is read operation.
 Transfer of new information to be stored into the
memory is called write operation.
 Memory word is symbolized by M and address by
enclosing in the square bracket.
 Read and write operation can be stated as:
 Read: DR M[AR]
 Write: M[AR] R1

20. Micro operations
 μ-operation is an elementary operation performed
with the data stored in register. They can be
classified as:
 Register transfer micro-operations
 Arithmetic micro-operations
 Logic micro-operations
 Shift micro-operations

22.  Arithmetic operation divide and multiply are not
listed in table as they are not included in the basic set
of micro-operations.
 Multiplication is implemented by addition and shift
operations.
 Division is implemented by subtraction and shift
operation.

23. Logic Micro-operations
 These operation consider each bit of register
separately and treat them as binary variables.
 Example exclusive-OR between R1 and R2 can be
symbolized as:

24.  Special symbol are used for logical operations.
 ˆ denote AND operation and ˇ denote OR operation.
 When + symbol occur in micro-operation it denote
arithmetic addition but in control signals it denote
the OR.

26. Shift Micro-Operations
 These are used for serial data transfer.
 The information transferred through the serial input
determines the type of shift.
 There are three types of shift:
 Logical
 Circular
 Arithmetic

27. Logical Shift
 It is the one that transfer 0 through the serial input.
 Symbol shl and shr are used to represent left logical
shift and right logical shift respectively.

28. Circular Shift
 It circulates the bits of the register around the two
ends without loss of information.
 It is represented as cil or cir for left and right circular
shift.

29. Arithmetic Shift
 It shift the signed binary number to left or right.
 Arithmetic shift left multiply the signed binary
number by 2.
 Arithmetic shift right divide the signed binary
number by 2.
 It must leave the sign bit unchanged.
 It is represented by ashl and ashr.

31. Arithmetic Logic Shift Unit
 Computer systems employ number of storage
register connected to common operational unit
called ALU(Arithmetic Logic Unit) to perform micro-operation.
 ALU is combinational circuit so transfer from source
to ALU and ALU to destination is done only in one
clock cycle.
 Shift micro-operation is performed in separate unit
or can be made part of overall ALU.