Micro Instructions Sequencer is a combination of all hardware for selecting the next micro-instruction address. The micro-instruction in control memory contains a set of bits to initiate micro operations in computer registers and other bits to specify the method by which the address is obtained.
Implementation of Micro Instructions Sequencer –
- Control Address Register(CAR) :
Control address register receives the address from four different paths. For receiving the addresses from four different paths, Multiplexer is used.
- Multiplexer :
Multiplexer is a combinational circuit which contains many data inputs and single data output depending on control or select inputs.
- Branching :
Branching is achieved by specifying the branch address in one of the fields of the micro instruction. Conditional branching is obtained by using part of the micro-instruction to select a specific status bit in order to determine its condition.
- Mapping Logic :
An external address is transferred into control memory via a mapping logic circuit.
- Incrementer :
Incrementer increments the content of the control address register by one, to select the next micro-instruction in sequence.
- Subroutine Register (SBR) :
The return address for a subroutine is stored in a special register called Subroutine Register whose value is then used when the micro-program wishes to return from the subroutine.
- Control Memory :
Control memory is a type of memory which contains addressable storage registers. Data is temporarily stored in control memory. Control memory can be accessed quicker than main memory.
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