SPI with display modules in Raspberry Pi - Step-by-Step Execution

Concept Flow - SPI with display modules

Start SPI Setup

↓

Configure SPI Pins

↓

Initialize SPI Bus

↓

Send Commands/Data to Display

↓

Display Updates

↓

End or Repeat

This flow shows how SPI communication is set up and used to send data to a display module step-by-step.

Execution Sample

Raspberry Pi

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 500000
spi.xfer2([0xAE])  # Display OFF command

This code opens SPI bus 0, device 0, sets speed, and sends a command to turn the display off.

Execution Table

Step	Action	SPI Bus State	Data Sent	Result
1	Open SPI bus 0, device 0	Bus open, mode default	None	SPI ready for communication
2	Set max speed to 500000 Hz	Bus open, speed=500000	None	Speed configured
3	Send command 0xAE (Display OFF)	Bus open, speed=500000	[0xAE]	Display receives OFF command
4	Close or continue communication	Bus open	None	Ready for next commands or close

💡 Communication ends or repeats for more display updates

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
spi	None	SpiDev object open	Speed set to 500000	Data sent [0xAE]	Ready for next commands

Key Moments - 3 Insights

Why do we set spi.max_speed_hz before sending data?

Setting spi.max_speed_hz configures how fast data is sent over SPI. Without it, the default speed might be too slow or too fast for the display. See execution_table step 2.

What does spi.xfer2([0xAE]) do exactly?

spi.xfer2 sends the list of bytes over SPI and waits for the transfer to finish. Here, it sends the command 0xAE to turn the display off. See execution_table step 3.

Can we send data without opening the SPI bus first?

No, the SPI bus must be opened with spi.open before sending data. Otherwise, communication will fail. See execution_table step 1.

Visual Quiz - 3 Questions

Look at the execution_table, what is the SPI bus speed after step 2?

A Default speed

B 500000 Hz

C 1000000 Hz

D 0 Hz

💡 Hint

Check the 'SPI Bus State' column at step 2 in execution_table

At which step is the command to turn the display off sent?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Data Sent' column in execution_table

If spi.open was not called, what would happen when sending data?

A An error occurs because SPI bus is not open

B Data sends normally

C Data sends but very slowly

D SPI bus opens automatically

💡 Hint

Refer to key_moments about opening SPI bus before sending data

Concept Snapshot

SPI with display modules:
- Open SPI bus with spi.open(bus, device)
- Set speed with spi.max_speed_hz
- Send commands/data with spi.xfer2([bytes])
- Commands control display behavior
- Always open bus before sending data

Full Transcript

This visual execution shows how to use SPI communication on a Raspberry Pi to control a display module. First, the SPI bus is opened with spi.open(0, 0). Then, the speed is set to 500000 Hz using spi.max_speed_hz. Next, a command byte 0xAE is sent to the display using spi.xfer2, which turns the display off. The variable 'spi' changes from None to an open SPI object, then has speed set, and finally sends data. Key points include setting speed before sending data, sending commands with xfer2, and opening the SPI bus first. The quiz checks understanding of these steps and their order.