by: Mr. Rodelio P. Barcenas
Faculty Computer Engineering Department
Don Bosco Technical College

Another Example:

Register C is an up/down counter register, while A and B are plain registers.

The above circuit can now be translated into an RTL. First we need to identify the control signals. It can be easily seen that S and D are control elements. Therefore we can now write;

S'D': A <-- B ; C <-- C + 1 {two operations exists}
S'D : A <-- B ; C <-- C - 1 {two operations exists}
S D': A <-- C + 1
S D : A <-- C - 1

Since now that we have two bit variables for the control elements, we have four possible combinations which will in turn give us four different RTLs. The more control elements, the more microoperations or RTLs that would represent the circuit.

At this point I suppose you are getting more curious about the relation of RTLs in microprocessors... I still need one more example and I will call this the punch line.

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