Pre-Execution state of Register/Memory Location values: PC: 35 Memory Location V
ID: 3602260 • Letter: P
Question
Pre-Execution state of Register/Memory Location values:
PC: 35
Memory Location
Value
35
901 (INPUT) [Assume user inputs “500” from keyboard]
36
181 (ADD 81)
37
383 (STORE 83)
38
901 (INPUT) [Assume user inputs “901” from keyboard]
39
583 (SUBTRACT 83)
40
902 (OUTPUT A)
41
HALT
81
400
82
000
83
000
* Note: 901 and 902 are instruction for input and output contents of Accumulator.
The following code is executed. Compute the result. Show the values of the registers in each of the following step. Mark Fetch/Execute Cycles within the code. Write a summary on what this program does.
Instruction: 901 (Input)
PC -> MAR
MDR -> IR
IOR -> A
PC+1 -> PC
Instruction: ADD 81
PC -> MAR
MDR -> IR
IR[address] -> MAR
A+MDR -> A
PC +1 -> PC
Instruction: STORE 83
PC -> MAR
MDR -> IR
IR[address] -> MAR
A -> MDR
PC+1 -> PC
Instruction: 901 (Input)
PC -> MAR
MDR -> IR
IOR -> A
PC+1 -> PC
Instruction: SUBTRACT 83
PC -> MAR
MDR -> IR
IR[address] -> MAR
A-MDR -> A
PC+1 -> PC
Instruction: 902 (OUTPUT A)
PC -> MAR
MDR -> IR
A -> IOR
PC+1 -> PC
// This is the halt instruction. Assume the content on that memory location is “HALT” and the system knows to halt the program when that instruction is loaded.
PC -> MAR
MDR -> IR
WHAT IS DISPLAYED AS THE FINAL ANSWER? __________
Memory Location
Value
35
901 (INPUT) [Assume user inputs “500” from keyboard]
36
181 (ADD 81)
37
383 (STORE 83)
38
901 (INPUT) [Assume user inputs “901” from keyboard]
39
583 (SUBTRACT 83)
40
902 (OUTPUT A)
41
HALT
81
400
82
000
83
000
Explanation / Answer
Instruction: 901 (Input)
PC -> MAR
MDR -> IR
IOR -> A
PC+1 -> PC
Instruction: ADD 81
PC -> MAR
MDR -> IR
IR[address] -> MAR
A+MDR -> A
PC +1 -> PC
Instruction: STORE 83
PC -> MAR
MDR -> IR
IR[address] -> MAR
A -> MDR
PC+1 -> PC
Instruction: 901 (Input)
PC -> MAR
MDR -> IR
IOR -> A
PC+1 -> PC
Instruction: SUBTRACT 83
PC -> MAR
MDR -> IR
IR[address] -> MAR
A-MDR -> A
PC+1 -> PC
Instruction: 902 (OUTPUT A)
PC -> MAR
MDR -> IR
A -> IOR
PC+1 -> PC
HALT
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