Lesson 6: SPI Communication - High-Speed Data Transfer

📌 Learning Objectives

1. Understand what SPI protocol is
2. Learn about SPI hardware connections
3. Understand differences between SPI and I2C
4. Learn to use SPI devices

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🎯 What is SPI?

SPI = Serial Peripheral Interface

A Useful Analogy

Imagine a meeting room:

• Master = The meeting host
• Slaves = Meeting participants (can be multiple)
• MOSI = What the host says
• MISO = The participants' responses
• SCLK = Meeting rhythm
• CS = Calling roll: Only the one called speaks

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🔌 SPI Hardware Connections

Requires 4 wires:

Wire Name	Full Name	Function
SCLK	Serial Clock	Clock line
MOSI	Master Out Slave In	Master output, slave input
MISO	Master In Slave Out	Master input, slave output
CS	Chip Select	Chip select (chooses which device to talk to)

Connection Diagram

Microcontroller      SD Card        OLED Screen
       │               │               │
       ├─ SCLK ───────┼─ SCLK ───────┤
       ├─ MOSI ───────┼─ MOSI ───────┤
       ├─ MISO ───────┼─ MISO ───────┤
       ├─ CS1  ───────┤               │
       └─ CS2  ───────────────────────┤

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📊 SPI vs I2C Comparison

Feature	I2C	SPI
Wires needed	2	4
Device addresses	Yes (7-bit/10-bit)	No (uses CS)
Speed	Slower (typically 400kHz)	Faster (up to several MHz)
Communication	Half-duplex	Full-duplex
Multiple devices	Shared addressing	Each device has independent CS
Complexity	More complex	Simple

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🎯 When to Use SPI?

Good for SPI:

1. Need high-speed transfer: Reading large amounts of data
2. SD card/W25Q storage: Fast read/write
3. Displays: Quick screen refreshes

Good for I2C:

1. Save pins: Not enough pins available
2. Many sensors: Temperature, humidity, light, etc.
3. Low-speed devices: Don't need high speed

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🔧 SPI Devices in JoyKit

Common SPI devices on JoyKit:

Device	Purpose
W25Q32	Flash memory (store data, images)
4.3" LCD	Main screen display
OLED	Secondary display

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🔬 Classroom Demo: Comparing I2C and SPI

Demo Goal

Experience the different characteristics of I2C and SPI.

Comparison	I2C Sensor	SPI Screen
Wires	Few	Many
Speed	Slow	Fast
Purpose	Read data	Write display

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💡 Memory Aids

Protocol	Characteristics
I2C	Few wires, has addresses, good for sensors
SPI	Many wires, fast speed, good for screens/storage

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🎉 Summary

What we learned today:

• ✅ SPI is Serial Peripheral Interface
• ✅ Needs 4 wires: SCLK, MOSI, MISO, CS
• ✅ SPI is faster than I2C
• ✅ I2C for sensors, SPI for screens/storage
• ✅ JoyKit has multiple SPI devices

Next will be comprehensive projects using everything we've learned!