Timing and Control

Timing of instructions-:

Every instruction needs some timing signals for its execution. The exact number of timing signal will depend upon how long it takes for an instruction to execute completely for example-: an instruction with a subroutine or a system call will require more timing signals than an ordinary instruction.


Subroutine here, is another instruction that has to be invoked in order to complete the parental instructions in computer definitions timing signals are used as conditions for example-:




T1:R2<-R1 states that the transfer will take place only when timing signal is 1.


Generation of timing signal-:



Although, we have two options to generate timing signal
1-: Using dedicated circuit
2-: Using a processor that continuously proce4sses increment kind of instruction.


As a legacy timing signals where generated in computers using dedicated circuit’s .A circuit of this kind as follows.



The circuit is good enough but limited specially because it can produce only 8 continuous timing signals Instead, we could have used another mechanism that uses the microprocessor a slight change in the instruction could have change the timing signals the processor was to generate

Timing diagram

A timing diagram is nothing but a plot of at which time the respected instruction will trigger the plot is basically made of vertical lines each lines representing significant time .the instruction are plotted by horizontal lines the plot of an instruction takes a rise on the appropriate time of trigger similarly takes a fall at the end of that time The rise and fall may be depend on some other conditions as well.



Control-:



Control is the other aspect that has serious influence on instruction execution .in most of the cases control is directly related to timing signal .in other words a condition based on time is like a control for the instruction to trigger. Now based on the two methods of generation of timing signal control is of two types older computer uses “Hard wired” control while modern computers use ” Micro-programmed Control”

Hardwired control-:



A hard wired control is based on a clear cut circuit which is limited in number of timing signal it generates.

Micro programmed -:

Micro-programmed control is the one that uses specially designed microprocessor induce flexibility in the number of timing signals it will generate.