Saint Louis University 
Computer Science 140

Dept. of Math & Computer Science 
Topic: Computer Architecture, LowLevel Programming with Meyer's Super
Simple CPU.
Related Reading: Ch. 5, Notes on the Super Simple CPU (abbreviated SSCPU)
Due:
8pm Tuesday, 4 March 2008
8pm Thursday, 6 March 2008
For this assignment, we will rely at times on the Simple Super CPU software demonstrated in class. You will need to have an Internet connection to run this software.
Exactly how many bytes are in 128MB?
What SSCPU instructions do NOT involve the accumulator?
Translate the following machine code to assembly language. Check using the
SSCPU.
0100000000000111
0101000000000101
0100000000000011
0001000000000101
1111000000000000
Play computer with the program above. Assume the remaining memory
cells are initialized to 0. Keep columns for the instruction number,
its corresponing opcode mnemonic and operand in decimal, the accumulator
value after the instruction executes, and the value of memory cell 5 after
the instruction executes:
#  Instruction  Accumulator  Mem 5 
Translate the following assembly language program into machine language. Check with the SSCPU.
GO INP SUB VAL JZR BYE JMP GO BYE STP VAL DAT 21
Play computer with the program below, assuming 2 is the input. Keep columns for the instruction number (or label), its corresponing opcode mnemonic and operand in decimal, the accumulator value after the instruction executes, and the value of the data N and P after the instruction executes:
0 LDI 3 1 STO P 2 INP 3 STO N TOP JZR BYE ; this is line 4 5 LOD P 6 ADD P 7 STO P 8 LOD N 9 SUB ONE 10 STO N 11 JMP TOP BYE STP ONE DAT 1 N DAT 0 P DAT 0
#  Instruction  Accumulator  N  P 
Although the SSCPU simulator only displays 16 memory cells, the instruction format could presumably utilize more memory. What is the largest number of memory cells that the SSCPU could effectively use without having to change the instruction format? Explain your answer.
Suppose the assembly program below is run and the sequence of instruction numbers executed is 0, 1, 2, 4. What number was input in the first instruction? Explain your answer.
GO INP SUB VAL JZR BYE JMP GO BYE STP VAL DAT 21
Write a sequence of machine code instructions to copy the data at memory location 13 to the output.
Write an assemblylanguage program that inputs two
numbers from the user and outputs the value
of the expression
Write an assemblylanguage program that inputs two numbers from the user and outputs the maximum of the two.
Overall, please type your answers to all of the problems in a single document to be submitted electronically. Please see details about the submission process.
The SSCPU has no instructions for multiplication, division or finding a remainder from division. These operations can be done using the existing instructions, by doing addition or subtraction in a loop. Write an assemblylanguage program which inputs positive numbers D and N and outputs the remainder of the dividing of D into N. For example if 5 and 15 were input, the output would be 0. If 7 and 19 were input, the output would be 5. (Of course all inputs and outputs are actually in binary.) Hint: Do this by repeated subtraction. If the remainder is 0, you will eventually end up with 0. If the remainder is not 0, you will probably need to subtract until the result is negative. In this case add D at the end to get the actual remainder. For the second example: 197=12, 127 = 5, 57 = 2, so add 7 back to get the remainder 5
Write an assemblylanguage program which inputs a positive number N and outputs 1 + 2 + 3 + ... + N, the sum of all the integers from 1 to N. For example, if 101 binary (5 decimal) were input, the output should be 1 + 2+ 3 + 4 + 5 = 15 decimal or 1111 binary. Hint: part of the challenge will be fitting your program into the limited memory of SSCPU. Try adding in the order from N down to 1.