Figure P7.3 gives part of the microinstruction sequence corresponding to one of the machine instructions of a microprogrammed computer. Microinstruction B is followed

by C, E, F, or I, depending on bits b6 and bs of the machine instruction register. Compare the three possible implementations described below.

(a) Microinstruction sequencing is accomplished by means of a microprogram counter. Branching is achieved by microinstructions of the form If b6b5 branch to X where b6b5 is the branch condition and X is the branch address.

(b) Same as Part a except that the branch microinstruction has the form Branch to X, OR where X is a base branch address. The branch address is modified by bit-ORing of bits bs and b6 with the appropriate bits within X.

(c) A field in each microinstruction specifies the address of the next microinstruction, which has bit-ORing capability. Assign suitable addresses for all microinstructions in Figure P7.3 for each of the imple- mentations in Parts a through

c. Note that you may need to insert branch instructions in some cases. You may choose arbitrary addresses, as long as they are consistent with the method of sequencing used. For example, in Part

a, you could choose addresses as follows:

Transcribed Image Text:

b6bs=00 C 01 D E A B J 10 G H