lecture4

Execution of Branch Instructions
? A branch instruction replaces the contents of PC with the branch target address, which is usually obtained by adding an offset X given in the branch instruction.
? The offset X is usually the difference between the branch target address and the address immediately following the branch instruction.
? Conditional branch
Microprogrammed Control
? An instruction is executed by carrying out a sequence of more rudimentary operations.
? All operations and data transfers are controlled by the processor clock.
? The ALU is a combinational circuit that has no internal storage.
? To execute instructions, the processor must have some means of generating the control signals needed in the proper sequence.
? Two categories: hardwired control and microprogrammed control
? Hardwired system can operate at high speed; but with little flexibility.

Control Unit Organization

? The previous organization cannot handle the situation when the control unit is required to check the status of the condition codes or external inputs to choose between alternative courses of action.
? Use conditional branch microinstruction.

Organization of the control unit to allow conditional branching in the microprogram