30-06-2012, 12:01 PM
Basic Computer organization and design
Basic Computer organization and design-II.pptx (Size: 291.18 KB / Downloads: 77)
CONTROL UNIT
Control unit (CU) of a processor translates from machine instructions to the control signals for the microoperations that implement them
Control units are implemented in one of two ways
Hardwired Control
CU is made up of sequential and combinational circuits to generate the control signals
It can be optimized to produce a fast mode of operation
Microprogrammed Control
A control memory on the processor contains microprograms that activate the necessary control signals
Easier to modify
We will consider a hardwired implementation of the control unit for the Basic Computer.
INSTRUCTION CYCLE
In Basic Computer, a machine instruction is executed in the following cycle:
Fetch an instruction from memory
Decode the instruction
Read the effective address from memory if the instruction has an indirect address
Execute the instruction
After an instruction is executed, the cycle starts again at step 1, for the next instruction
Note: Every different processor has its own (different) instruction cycle