The control unit
We have seen that the activity of the computer is determined by the instructions that are stored in memory as patterns of 0s and 1s. In this chapter, we consider two approaches to the design of the control unit within the G80 microprocessor. The first approach results in a hard-wired controller, while the second results in a micro-programmed controller. We begin by asking what the control unit must do.
13.1 Requirements of the control unit
In order to process a particular instruction the G80 must first fetch the instruction from memory and then execute that instruction. In the fetch phase the operation code at the memory location pointed to by the Program Counter is read and transferred into the Instruction Register, IR. ...
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