An Example Super Simple Machine Program
Problem
Write a machine code program to write zeros into memory. The start address is
given at address 0x80 and the number of words to write is given at address
0x84. We assume the start address is word aligned and the number of words to
write is greater than zero.
Pseudocode (optional)
Write out each step your assembly language program needs to do. You can skip
this if you find yourself writing assembly code.
R0 = 0x80 (address of start address)
R0 = memory[R0] (current address)
R1 = 0x84 (address of number of words)
R1 = memory[R1] (number of words)
R2 = 0x0 (constant 0)
R3 = 0x4 (constant 4)
R4 = 0x0 (number of words written to)
R5 = 0x1 (constant 1)
store R2 in memory[R0]
R0 = R0 + R3
R4 = R4 + R5
if (R4 != R1) branch to the store instruction (address 0x20)
Assembly Code
Translate the pseudocode from above if necessary into assembly code.
IMM R0, 0x80
LOAD R0, R0
IMM R1, 0x84
LOAD R1, R1
IMM R2, 0x0
IMM R3, 0x4
IMM R4, 0x0
IMM R5, 0x1
STORE R0, R2
ADD R0, R0, R3
ADD R4, R4, R5
BNE 0x20, R4, R1
Machine Code
Translate the assembly code into machine code using this chart:
| Operation | Opcode | Meaning of other bytes |
| ADD | 0x20 | Dest. reg. | Reg. 1 | Reg. 2 |
| IMM | 0x60 | Dest. reg. | Unused | Value |
| BNE | 0x11 | Dest. address | Reg. 1 | Reg. 2 |
| LOAD | 0xA4 | Dest. reg. | Reg. with address | Unused |
| STORE | 0x08 | Unused | Reg. with dest. address | Source reg. |
0x 60 00 00 80
0x A4 00 00 00
0x 60 01 00 84
0x A4 01 01 00
0x 60 02 00 00
0x 60 03 00 04
0x 60 04 00 00
0x 60 05 00 01
0x 08 00 00 02
0x 20 00 00 03
0x 20 04 04 05
0x 11 20 04 01
CSE 378 Spring 2002 - Section 2