O5. Assume a computer having 3L registers and a main memory that are connected t
ID: 3594971 • Letter: O
Question
O5. Assume a computer having 3L registers and a main memory that are connected through a common bus. Assume the computer ALU can perform 1 different operations (arithmetic, shift and logic operations). The control signals are Load, Clear, and Increment controls for each register, memory read and write signals, bus select signals and ALU operation control signals. Assume the design has 250 distinct control words. Assume also that each microinstruction requires t for branch condition and branch type (i.e., similar to the CD and BR bits used in your textbook) a. b. c. d. What is the size of the control store if you use a pure horizontal microinstruction format? What is the size of the control store if you use a pure vertical microinstruction format? Which one of the above two options will be more costly in terms of chip area? Which one of the above two options will produce a faster control unit?Explanation / Answer
a) In horizontal microinstruction format, each control signal is represented by a single bit in the control word, hence for 250 distinct control words, the size of control store will be 250 bits.
b) In vertical microinstruction format, thw width of the control word is narrow and n control signals are encoded in log2n control bits, and here n = 250.
So, calculating the size of control store as,: log2 250
: log 250 / log 2
: 8 bits
c) In case of horizontal microinstruction format the memory word used is wide and detailed while for vertical microinstruction format, the memory word is comaparably small, so the cheap area cost is gretaer in case of horizontal microinstruction format.
d) Horizontal microinstruction format supports parallalism, i.e, execution of multiple instruction at a time, while execution of a single instruction takes place in case of verticle microinstruction format, hence horizontal microinstruction format produce a faster control unit.
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