MPLAB v8, MPLAB X, Proteus, and board

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So far you learned what to write in assembly (MPASM), how the configuration word works (config bits), and the PIC minimum system. This page closes Foundations: which tools you use to build, simulate, and test in the UNEXPO course.

The academic workflow focuses on MPLAB v8 + MPASM + Proteus. You will also see MPLAB X so you recognize the modern IDE on another machine.

Real workflow

Write .ASM in MPLAB → MPASM produces .HEX → load .HEX in Proteus (simulation) or a programmer (physical board) → compare behavior with what you expect.

What MPLAB is (and what it is not)

Reports and labs mix three names. Keep them separate:

Tool	What it is	Course role
MPLAB v8 / X	IDE — development environment	Edit .ASM, create project, run build, program with PICkit
MPASM	Assembler	Translates .ASM → .HEX (program + configuration word)
Proteus ISIS	Simulator	Runs .HEX in a virtual circuit — does not compile
PICkit / programmer	Burner	Writes .HEX to real PIC Flash

MPLAB is not the assembler. MPLAB is the workspace; when you click Build, MPLAB calls MPASM for you.

Step 1 — Write the .ASM in MPLAB

Create a PIC18F4550 project and edit source using the sandwich layout: LIST, #include, CONFIG, ORG, subroutines, programa: at the bottom.

The file on disk is plain text (.ASM / .asm). MPLAB saves and highlights it — there is no .HEX yet.

Step 2 — Build with MPASM

Project → Build All invokes MPASM. If there are no errors, you get the .HEX:

  your_program.ASM
       ↓  MPASM (from MPLAB)
  your_program.HEX   ← Flash program + config bits
  your_program.COD   ← listing (optional, debug)

If END is missing, a symbol lacks #include, or a label is wrong, the build fails — do not simulate until you fix the Output window.

Step 3 — Simulate in Proteus

Wire the minimum system + LED, load the same .HEX into the virtual PIC, and press Play. Proteus interprets .HEX bytes; it does not read your .ASM directly.

Step 4 — Physical board

With the same .HEX (rebuilt if you changed code), connect PICkit, Program in MPLAB, and validate the LED or peripheral on the breadboard.

Course golden rule

Build without errors → simulate in Proteus → breadboard. Not the other way around. Proteus never replaces MPASM.

What the .HEX file contains

The .HEX is the bridge between software and hardware. It is not readable .ASM — Intel HEX format with two conceptual blocks:

.HEX content	Source in your .ASM	Destination
Program (instructions)	ORG, GOTO, MOVLW, BSF…	Executable Flash
Configuration word	CONFIG directives	Config memory (startup)

One file feeds Proteus and the programmer: both need program and config bits matching the 20 MHz crystal and course template.

Full chain — from text to the PIC

  MPLAB editor (.ASM)
       ↓  Build / assemble
  MPASM → .HEX file (+ optional .cod)
       ↓
  ┌────────────────┴────────────────┐
  ↓                                 ↓
Proteus (simulation)          PICkit / programmer
  ↓                                 ↓
Virtual LED, logic pins       UNEXPO physical board

Stage	Tool	Input	Output
Write	MPLAB v8 / X	Your source code	.ASM
Assemble	MPASM	.ASM	.HEX (program + config bits)
Simulate	Proteus ISIS	.HEX + schematic	Virtual behavior
Program	PICkit 2/3, etc.	.HEX	PIC18F4550 Flash

Full walkthrough — minimal example (First LED)

Suppose you turn on RB0. The full flow:

1. Source in MPLAB — minimal fragment (see Assembly — LED):

        LIST    P=18F4550
        #include <P18F4550.INC>
        CONFIG  FOSC = HS, WDT = OFF, LVP = OFF, PBADEN = OFF

        ORG     0x0000
        GOTO    programa         ; jump to main

programa:
        BCF     TRISB, 0
        BSF     LATB, 0
loop:
        GOTO    loop               ; jump → destination loop: (above)

        END

2. Build in MPLAB → project.hex appears with no errors in Output.

3. Proteus — PIC18F4550 + 20 MHz crystal + LED on RB0 → Program File = that .HEX → Clock Frequency = 20 MHz → Play.

4. Board — same .HEX, PICkit, Program → LED on if wiring and config bits match.

If you change one .ASM line, go back to step 2 before Proteus or the board. An old .HEX is the #1 cause of “simulation does not show my change”.

MPASM — what happens when you build

MPASM reads your assembly file and:

1. Translates mnemonics (MOVLW, BSF…) into machine code.
2. Resolves labels, #include symbols, and CONFIG directives.
3. Generates the .HEX for programmer or Proteus.
4. Reports errors if END is missing, labels duplicate, or symbols are undefined.

Files you see after a build

File	Purpose
.HEX	Load into Proteus or programmer — the important one
.COD	Listing with addresses and machine code (debug)
.LST	Source mixed with listing (if enabled)
.ERR	Assembly errors (if build fails)

If the build fails, there is no useful .HEX — fix errors in the output window before simulating.

MPASM errors you will see in MPLAB

Output message	Common cause	Review
Symbol not defined	Missing #include <P18F4550.INC> or typo (TRISB)	Assembly — directives
Label required	Label without : (programa vs programa:)	Labels
END directive required	Missing END at end	Sandwich layout
Bank select error	Variable in another bank without BSR	Registers — banks
Argument out of range	Literal outside 0–255	Literals

Next step on the path

After this page, the study path takes you to the ports practical guide and the First LED tutorial, where you create the MPLAB project and simulate in Proteus step by step with screenshots.

MPLAB v8 project — what the wizard creates

The Project Wizard does not write code for you; it organizes files and tells MPASM which MCU and tool to use:

Project element	Function
PIC18F4550 device	MPASM generates correct opcodes for that chip
MPASM toolchain	Not XC8 if the course is pure assembly
Added .asm file	Source you build
Project folder	Where .HEX appears after Build All

After building, find the .HEX in the project folder (sometimes Debug/, sometimes root). That path is what you load in Proteus → Program File.

MPLAB v8 — main course IDE

MPLAB v8 is Microchip’s classic IDE. UNEXPO labs often use it because it fits MPASM and pure .ASM projects well.

Where to download MPLAB v8

Microchip no longer lists MPLAB v8 on its main tools page, but keeps older releases in the official archive: MPLAB Ecosystem Archives. From there you can download MPLAB IDE v8 and related tools (including MPASM). Check compatibility with PIC18F4550 and your operating system.

MPLAB v8 — step by step

Create a project

1. Project → Project Wizard
2. Select PIC18F4550
3. Tool: MPASM (not XC8 if you only use assembly)
4. Project name and folder
5. Add your .asm file to the project

Build

1. Project → Build All (or hammer icon)
2. Check Output — should say Build succeeded
3. Find the .hex in the project folder (e.g. Debug/ or root)

Config bits in MPLAB v8

You can edit them via Configure → Configuration Bits, but in the course it is better to declare them in .ASM (config bits) so report and .HEX match.

Typical build errors

Message	Common cause
Symbol not defined	Missing #include <P18F4550.INC> or typo in TRISB
Label required	Label without : (start vs start:)
END directive required	Missing END at file end
Bank select error	Variable in another bank without correct BSR

MPLAB X

When to use it

MPLAB X is the modern IDE (NetBeans-based). Microchip promotes it for new XC8 projects, but it can assemble .ASM with the right toolchain.

Summary steps

1. File → New Project → Standalone Project
2. Device: PIC18F4550
3. Pick a toolchain compatible with assembly
4. Add your .asm to the project
5. Production → Build Main Project
6. Check Output and locate the .hex

If your instructor requires MPLAB v8, do not mix v8 and X projects in the same folder — paths and settings differ.

Proteus

Build the circuit

1. Place PIC18F4550 on the schematic
2. Wire minimum system: 20 MHz crystal, capacitors, MCLR pull-up, VDD/VSS, decoupling
3. Add LED + resistor on RB0 (or your lab pin)
4. Check common ground and LED polarity

Load the .HEX

1. Double-click the PIC → Program File tab
2. Select the .hex from MPASM
3. Set Clock Frequency to 20 MHz (matches FOSC = HS and crystal)
4. OK and save schematic

Run simulation

1. Play (Run simulation)
2. Watch virtual LED and RB0 levels
3. Use Debug to inspect registers if your version allows
4. If it does not start: check loaded .HEX, clock frequency, and config bits

Proteus does not assemble — it only runs the .HEX you built in MPLAB.

Physical board

Before programming

1. Stable 5 V supply and decoupling cap
2. 20 MHz crystal + caps + MCLR 10 kΩ (minimum system)
3. Check LED wiring (220–330 Ω resistor)
4. No shorts on the breadboard

Program the MCU

1. Connect PICkit 2/3 (or lab programmer) to ICSP
2. In MPLAB: Programmer → Select Programmer
3. Program with the same .HEX used in Proteus
4. Confirm Programming/Verify complete

Validate

1. LED on/off per your code
2. Multimeter on output pins if something fails
3. Compare with simulation — Proteus OK but board not → suspect hardware (wiring, supply, wrong config bits)

MPLAB vs Proteus vs board — who does what

Task	MPLAB + MPASM	Proteus	Physical board
Write code	✅	❌	❌
Build .HEX	✅	❌	❌
Simulate without hardware	❌	✅	❌
Real crystal timing	❌	Approximate	✅
Noise, contacts, bounce	❌	Limited	✅
Program PIC Flash	With programmer	Simulates only	✅

Course rule: build without errors first, then simulate in Proteus, then breadboard.

Cross-tool consistency — checklist

Before saying “it does not work”, verify everything matches:

• Device: PIC18F4550 in MPLAB, Proteus, and board
• CONFIG FOSC = HS and 20 MHz crystal in schematic and Proteus
• Same .HEX in Proteus and programmer (rebuild after every change)
• PBADEN = OFF, LVP = OFF, WDT = OFF (course template)
• LED pin matches code (RB0 → BCF TRISB,0 and BSF LATB,0)
• Rebuilt after editing .ASM

Ejercicio · Parcial

Order the workflow

Correct order for the First LED practice:

1. Write .ASM with LIST, #include, CONFIG, ORG, GPIO code
2. Build in MPLAB → get .HEX
3. Build schematic in Proteus with 20 MHz crystal
4. Load .HEX into Proteus PIC
5. Simulate and verify LED
6. Breadboard and program with PICkit

Typical mistake: loading an old .HEX in Proteus after changing code without rebuilding — simulation does not reflect your latest changes.

Common mistakes

• Proteus without loaded .HEX: PIC simulates empty memory or old program.
• Proteus clock not 20 MHz: timing and some peripherals won’t match the board.
• Mixing MPLAB X and v8 projects: conflicting paths and toolchains.
• Simulation OK, board not: check supply, MCLR, crystal, PIC orientation, LVP/PBADEN.
• Board OK, simulation not: outdated .HEX or wrong Proteus frequency.
• Treating Proteus as compiler: Proteus does not replace MPASM — it only runs .HEX.

Exam-style questions

What is the difference between MPLAB and MPASM?

MPLAB is the environment (editor, project, programmer). MPASM is the assembler that translates .ASM → .HEX when you Build.

What file does MPASM produce on a successful build?

A .HEX file with program and config bits for programming or simulation.

What is Proteus used for in the course?

To simulate circuit and program before the physical board, loading the .HEX from MPLAB.

Does MPLAB assemble directly or use another tool?

MPLAB invokes MPASM (for pure assembly projects in the course).

Why must Proteus clock frequency match the crystal?

Execution time and peripherals depend on Fosc; with FOSC = HS and 20 MHz crystal, Proteus should use 20 MHz.

Interactive exam

MPLAB and Proteus

0 of 0 answered

In the course workflow, Proteus is mainly used to...

Simulate the circuit before the physical board Compile C++ for Linux Burn EEPROM only Configure ESP32 Wi-Fi

MPASM mainly produces a...

.hex to program or simulate the PIC .pdf report .exe for Windows .json config

The correct academic workflow order is...

Write .ASM → build .HEX → simulate in Proteus → physical board Proteus → write .ASM → build without MPLAB Physical board → then write code Simulate only without building

In Proteus, the PIC clock frequency should match...

The schematic crystal (e.g. 20 MHz with FOSC=HS) The PC speed in GHz UART baud rate always 9600 The .ASM file size

Proteus CANNOT...

Compile MPASM assembly to .HEX Load a .HEX file into the virtual PIC Simulate an LED on RB0 Show logic levels on pins

In course MPLAB v8, the assembly tool is...

MPASM XC8 only Proteus VSM Git

If you change .ASM but do not rebuild, in Proteus...

Simulation may show an old program MPASM rebuilds automatically The PIC reprograms itself Proteus edits .ASM for you

To program the UNEXPO physical board you use the same...

.HEX generated by MPASM .PDF report Proteus schematic without building Only the .INC file

Simulation OK but board fails — check first...

Power, crystal, MCLR, and hardware wiring Reinstall Windows Change the quiz slug Delete the .HEX

The .HEX also contains besides the program...

Config bits defined with CONFIG Only .ASM comments Full readable source code User EEPROM

MPLAB v8 by itself...

Is the IDE; MPASM assembles when you Build Compiles .ASM to .HEX without MPASM Replaces Proteus for simulation Automatically programs user EEPROM

You change one .ASM line but do not rebuild. In Proteus...

Simulation may still show the old program from the previous .HEX Proteus rebuilds .ASM automatically The virtual PIC edits your source for you It does not matter; Proteus reads .ASM directly

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