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EEE120 Lab 4: The Architect's Guide

EEE120 Lab 4: The Architect's Guide












EEE120 Lab 4 Cheat Sheet

Mastering the Control ROM & Writing Test Programs










What does "Making a Test" mean?




You are building a programmable computer. To "test" it, you have to wear two different hats:







1. The Architect (ROM)
You teach the CPU how to do a task. You define the "AND" instruction by flipping bits in microprocessor.v (the ROM).









2. The Programmer (RAM)
You ask the CPU to perform that task. You write a list of numbers in ram_vals.txt that forces the CPU to run your new instruction.









// The Workflow

Step 1: Modify ROM (Define Instruction)

-> Set control bits for 'AND' at address 12 (0xC)

Step 2: Modify RAM (Write Program)

-> 0 // Load

-> 3 // Value 3

-> C // Run the 'AND' instruction

-> ...

Step 3: Simulate (iverilog)













The Control Word Decoder

When editing my_rom[x] = 14'h...., you are setting these bits. This is Table 3 from your manual, visualized.






Bit

Name

Function






13:12

Next Step

01=Go to Step 1, 00=Done (Fetch Next)




11:10

Unused

Always 00




9

use_pc

1=Next Instruction, 0=Use MAR (Data)




8

load_mar

1=Save Data Bus to Address Register




7

arith

1=Add/Sub, 0=Logic




6

invert

1=Invert Input A (for Subtract)




5

pass

1=Pass Data (No math), 0=Do Math




4

load_acc

1=Save result to Accumulator




3

acc_to_db

1=Put Accumulator on Data Bus




2

read

1=Read from RAM




1

write

1=Write to RAM




0

load_ir

1=Load New Instruction (Fetch)















Task 4-5 Solutions

Use these logic values to build your hex codes.




1. AND Instruction
ALU does "AND" when Arith=0, Pass=0.


Arith: 0
Invert: 0
Pass: 0







2. ZERO Instruction
Subtract Accum from itself. (A - A = 0)


Arith: 1
Invert: 1
Cin: 1 (via carry)







3. STORE Instruction
Needs 2 Steps! 1. Load address into MAR.2. Write Accum to RAM.












How to write 'ram_vals.txt'

Task 4-5 Check






To prove your new instructions work, you need to write a program that uses them.…