CPU Signals Problem

CPU Signals Problem
	CSc 314 Study Material

Exam II may have a question like this one:

Consider the diagram in Figure 5.33 on p. 383. Assume that the CPU is executing the instruction

sw $8, 180($29)

Fill in the value of each indicated signal at the end of each cycle. If a control signal does not matter, record an X. If a data signal is unknown, record an X. Assume the memory cannot both read and write during the same cycle.

Signal Cycle 1 Cycle 2 Cycle 3 Cycle 4

PCWriteCond

PCWrite

MemRead

. . .

And you are invited to fill out the blanks.

Here's the answer to that one:

Signal	Cycle 1	Cycle 2	Cycle 3	Cycle 4
PCWriteCond	0	0	0	0
PCWrite	1	0	0	0
IorD	0	X	X	1
MemRead	1	X	X	0
MemWrite	0	0	0	1
MemtoReg	X	X	X	X
IRWrite	1	0	0	0
PCSource	0	X	X	X
ALUOp	00	00	00	XX
ALUSrcB	01	11	10	XX
ALUSrcA	0	0	1	X
RegWrite	0	0	0	0
RegDst	X	X	X	X
Instruction[5-0]	XXXXXX	110100	110100	110100
Read register 2	XXXXX	01000	01000	01000