The following experiment will acquaint you with the simulation program.

Experiment 4.1

Familiarize yourself with SimpSim by following the steps below to enter and execute the following

machine language program.

Address Content

10 23

11 FF

12 12

13 10

14 50

15 23

16 30

17 40

18 C0

19 00

Step 1. Start SimpSim and enter the program by typing the following

data in the Main Memory window.

[10] 23 FF 12 10 50 23 30 40 C0 00

Step 2. Set the program counter to 10 by typing the following line in the Program Counter window.

[PC] 10

Step 3. Inspect the Main Memory display to confirm that the program has been properly

placed in memory starting at location 10 and that the program counter is set at 10.

Then, execute a single machine cycle by clicking the Step button

. What is the value of the program counter at this point? _______

What is the value in register 3 at this point? _______

Step 4. Click the Run button to continue executing the program until a halt instruction is reached.

What is the value of the program counter when the simulation halts? __________

What is the value in memory cell 40 when the simulation halts? _________

Step 5. Translate the program in this experiment into English and confirm that the simulator

performed the appropriate actions.

Step 6. Change the contents of the memory cell at address 14 to the hexadecimal value 60.

Then, execute this modified program by changing the program counter back to 10 and

clicking the Run button. Explain the difference in the actions of this program from those of

the original program.

< Finish explanation on back if necessary. >

Machine-Level Instructions

In the following experiments, you will examine some of the instructions found in a traditional

machine language.

Experiment 4.2

In this experiment you will investigate the various arithmetic and logic operations available on

the machine simulated by the application SimpSim.

Step 1. Clear the simulator's main memory and registers. Then, place the value 5C in register 1

and the value 3F in register 2. Finally, place the values 50 and 12 at memory locations A0

and A1, put the value A0 in the program counter, and execute a single machine cycle. Record

the value left in register 0 and explain this result.

Step 2. Place the value 60 at memory location A0, reset program counter at A0, and execute a

single machine cycle. Repeat this process using the values 70, 80, and 90. In each case record

the value that is placed in register R0 and explain the result.

Experiment 4.3

In this experiment you will investigate an application of masking.

Step 1. Start SimpSim and clear the simulated machine's main memory. Place the program below in the

memory cells from address 00 to 1D. Then, place the values 6F, 87, D0, 5E, 29, and 90 in the cells from

address A0 to A5.

Address Contents Address Contents

00,01 20,80 10,11 54,34

02,03 11,A0 12,13 34,03

04,05 81,10 14,15 34,0B

06,07 B1,0C 16,17 20,A6

08,09 22,00 18,19 B4,1C

0A,0B 32,A0 1A,1B B0,00

0C,0D 23,01 1C,1D C0,00

0E,0F 14,0B

Step 2. Run the program and record the changes in the values stored from address A0 through

A5. Assuming that the patterns represent values stored in floating-point notation, state a

general rule for determining which patterns are replaced by zeros. (Look at the sign bit of the

original patterns.)

Step 3. Alter the program so that it replaces only the negative values with zeros and test your

program. Record the changes you made below.

Experiment 4.4

In this experiment you will investigate the branch instruction found in the machine language

for the machine simulated by SimpSim.

Step 1. Start SimpSim and clear the simulated machine's main memory. Then, place the program

below in the memory cells from address F0 to FD.

Address Contents Address Contents

F0 20 F7 FC

F1 00 F8 50

F2 21 F9 01

F3 01 FA B0

F4 23 FB F6

F5 05 FC C0

F6 B3 FD 00

Step 2. Execute the program one step at a time by clicking the Single Step button. Record the

values of the program counter after each step.

Step 3. Explain the results obtained in Step 2.

Step 4. What changes should be made to the program in Step 1 if it were to be placed in

memory starting at location A0? Explain your answer.