computer organization and archietecture CO COA

1. Computer Organization
PRESENTED BY :
SHARDUL DAVE (130110107003)
YASH DOSHI (130110107004)
Faculty :
Prof. Kinjal Joshi
Gujarat Technological University
G.H Patel College of Engineering and Technology
Department of Computer Engineering

2. Control Unit
The control logic is implemented with gates, F/Fs, decoders, encoder digital
circuits
Advantage :Fast operation.
Disadvantage :Wiring change(if the design has to be modified)
»Hardwired Control :
• Two major types of Control Unit
•Initiate sequences of microoperations

3.  The control information is stored in a control memory, and the control memory is
programmed to initiate the required sequence of microoperations
 Advantage :Any required change can be done by updating the microprogram in control
memory.
 Disadvantage :Slow operation
»Microprogrammed Control :

4. Control Word
• As per the operation, certain micro-operations are to be initiated, while
others remain idle at given time.
• These control variables at any given time can be represented by a string of 1’s
and 0’s is called as control word.
• A control unit whose binary control variables are stored in memory
(control memory).
Microprogrammed Control Unit
Microinstruction
• The microinstruction specifies one or more micro-operations

5. Microprogram
A sequence of microinstruction
• RAM can be used for writing (to change a writable control memory)
• Microprogram is loaded initially from an auxiliary memory such as a
magnetic disk
• Control words in ROM are made permanent during the hardware
production.
»Dynamic microprogramming :Control Memory =RAM
»Static microprogramming : Control Memory =ROM

6. Control Memory
»A memory is part of a control unit.
»Computer Memory employs a microprogrammed control unit.
•Main Memory : for storing user program (Machine instruction/data)
•Control Memory : for storing microprogram (Microinstruction)

7. Microprogrammed Control Organization
Next-address
generator
(sequencer)
Control address
register
Control memory
(ROM)
Control data
register
Control
word
Next-address information
External
input

8. Control Address Register
Sequencer
Specify the address of the microinstruction
It holds the microinstruction read from memory
Determine the address sequence that is read from control memory
Next address of the next microinstruction can be specified several way depending
on the sequencer input.
• Hold the microinstruction read from control memory
• Allows the execution of the microoperations specified by the control
word simultaneously with the generation of the next microinstruction
Control data register

9. Address Sequencing
• Microinstructions are stored in control memory in groups, with each group
specifying a routine.
• Each computer instruction has its own microprogram routine in control
memory to generate the micro-operation that execute the instruction.
• The hardware that controls the address sequencing of the control memory
must be capable of sequencing the micro-operation within a routine and be
able to branch from one routine to another.
• When all execution of the instruction is completed, control must return to the
fetch routine.
• This is accomplished by executing an unconditional branch microinstruction to
the first address of the fetch routine.

10. The address sequencing capabilities required in a control memory are:
1. Incrementing of the control address register
2. Unconditional and conditional branches
3. A mapping process from the bits of the machine instruction to an
address for control memory
4. A facility for subroutine call and return

11. Mapping of Instructions

12. Mapping from instruction code to microinstruction address

13. Selection of address for control memory

14. Conditional Branching

15. THANK YOU…!