Lesson 3: IO Input/Output - Let the Microcontroller Talk to the World

📌 Learning Objectives

1. Understand what IO ports are
2. Learn to configure IO as input or output
3. Master digital output instructions
4. Master digital input instructions
5. Build a button-controlled LED project

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🎯 What is IO?

IO is short for Input/Output.

• Input: Microcontroller reads information from the outside world (buttons, sensors, etc.)
• Output: Microcontroller sends information to the outside world (LEDs, buzzers, etc.)

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🔧 Configuring IO Ports

Use register R25 to configure each IO port:

R25 Value	Description
0000	All set to output
00FF	All set to input
00F0	Lower 4 bits output, upper 4 bits input
000F	Lower 4 bits input, upper 4 bits output

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💡 Digital Output (0x01)

Control output devices like LEDs and buzzers.

Instruction Format

Instruction	OP00	OP01	OP10	OP11
01	00	Output pin (00~07) or FF (bitwise)	00	Output value

说明：

• Single pin output: OP01 = 0007 (specify LED0LED7), OP11 = 00 (ON) or 01 (OFF)
• Bitwise output: OP01 = FF, OP11 = 00~FF (each bit corresponds to an LED state)

Example: Control 8 LEDs

📚 With Comments

000 10 0019 0000  ; R25 = 0x0000 → All set to output
001 01 00FF 0001  ; 1st LED on (bitwise)
002 02 03E8 0000  ; delay
003 01 00FF 0002  ; 2nd LED on (bitwise)
004 02 03E8 0000  ; delay
005 01 00FF 0004  ; 3rd LED on (bitwise)
006 02 03E8 0000  ; delay
007 01 00FF 0008  ; 4th LED on (bitwise)
008 02 03E8 0000  ; delay
009 0E 0001 0000  ; loop back to 001

📋 Clean Code

000 10 0019 0000
001 01 00FF 0001
002 02 03E8 0000
003 01 00FF 0002
004 02 03E8 0000
005 01 00FF 0004
006 02 03E8 0000
007 01 00FF 0008
008 02 03E8 0000
009 0E 0001 0000

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🔍 Digital Input Jump (0x0B)

Read input devices like buttons and switches, and jump based on state.

Instruction Format

Instruction	OP00	OP01	OP10	OP11
0B	Condition	Jump address	00	00

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🔬 Classroom Demo Project: Button Controlled LED

Project Goal

LED on when button pressed, LED off when button released.

Hardware Connections

• Button: Connected to IO0 (input)
• LED: Connected to IO4 (output)

Reference Program

📚 With Comments

; Button-controlled LED project
000 10 0019 0001  ; R25 = 0x0001 → IO0 input, others output
001 0B 0001 0004  ; If IO0 is 1 (button released), jump to 004
002 01 0010 0000  ; LED on
003 0E 0001 0000  ; jump back
004 01 0000 0000  ; LED off
005 0E 0001 0000  ; jump back

📋 Clean Code

000 10 0019 0001
001 0B 0001 0004
002 01 0010 0000
003 0E 0001 0000
004 01 0000 0000
005 0E 0001 0000

Teaching Suggestions

• Add delays to make the LED blink when pressed
• Use multiple buttons to control multiple LEDs
• Try toggling state with a single press instead of holding

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💡 Understanding IO Output Data

Each bit of output data corresponds to one IO port:

Data Bit	Corresponding IO
Bit 0	IO0
Bit 1	IO1
Bit 2	IO2
...	...
Bit 7	IO7

Examples:

• 0001 → IO0 outputs high
• 0003 → IO0 and IO1 output high
• 00FF → All IO ports output high

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🎉 Summary

What we learned today:

• ✅ IO = Input/Output
• ✅ Configure IO direction with R25
• ✅ Instruction 0x01 outputs data
• ✅ Instruction 0x0B jumps based on input
• ✅ Completed button-controlled LED project

Next lesson, we'll learn about PWM to make LEDs breathe!