4. Consider Microprogram store shown in image below a. Why is the PC being place
ID: 3769658 • Letter: 4
Question
4. Consider Microprogram store shown in image below
a. Why is the PC being placed into the MAR at address 0000000?
b. What does the statement at address 0000001 have to do with executing an instruction?
c. Why is the PC incremented at address 0000010?
d. What assembly language instruction is the if statement at address 0001000 checking for? Explain how you know.
MicroOp1 MicroOp2 Jump AddressS Des NOP NOP NOP NOP 0000010 PC PC 0000011 MAR 1 R [11-0] 0000100 E IR (35-12) 1000 MicroOP2(4-1 Micro0P2(4-1 0000110 E IR (15-12) 0000101E TRIS 2 00010 00100 00110 01000 0101010 10110 10113 Micro0P2(4-1 0000111 IF IR (15-121 MicroOP2 4-1 0001000 I IRE5-121 MAR X MBR AC NOP NOP NOP NOP NOP 0101010 01., 1011 |M[MAR ]Explanation / Answer
4)
a) Address: 0000000
MicroOp1: MAR <-- PC
MicroOp2: NOP
Jump :0
Dest : 0000000
Here PC(Porgram Counter) will start fetch the instruction when MARIE id booted up, hardware sets the microsequencer to point to address 0000000 of the Microprogram . Execution commences from this entry point.
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b)
Address: 0000001
MicroOp1: IR <-- M [MAR]
MicroOp2: NOP
Jump :0
Dest : 0000000
here IR (INstruction Register) gives memory location to MARIE it has been adreess location 0000001 and then excute the instuction for do decoding.
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c)
Address: 0000010
MicroOp1: PC <-- PC + 1
MicroOp2: NOP
Jump :0
Dest : 0000000
here Program Counter(PC) will start excuteing statements one by one because INC the results of setement 2 is IR <-- M[MAR] so PC + 1.
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