SPI with display modules in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does SPI stand for and what is its main purpose in Raspberry Pi display modules?

SPI stands for Serial Peripheral Interface. It is a way for the Raspberry Pi to talk quickly with display modules by sending data one bit at a time over a few wires.

beginner

Name the four main wires used in SPI communication with display modules.

The four main wires are: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCLK (Serial Clock), and CS (Chip Select). For displays, MISO is often not used.

intermediate

Why do SPI display modules often require a 'Data/Command' pin?

The Data/Command pin tells the display if the information sent is a command (like 'clear screen') or actual data (like pixels to show). This helps the display understand what to do.

beginner

What Python library is commonly used on Raspberry Pi to control SPI displays?

The 'spidev' library is commonly used to control SPI devices, including display modules, on Raspberry Pi.

beginner

How do you enable SPI on a Raspberry Pi before using SPI display modules?

You enable SPI by running 'sudo raspi-config', navigating to 'Interface Options', then enabling SPI. After reboot, SPI pins become active for use.

Which SPI wire sends data from Raspberry Pi to the display?

A MOSI

B MISO

C SCLK

D CS

MOSI stands for Master Out Slave In, so it sends data from the Raspberry Pi (master) to the display (slave).

What is the role of the Chip Select (CS) pin in SPI communication?

A It provides power to the display

B It resets the display

C It selects which device to communicate with

D It sends clock signals

The CS pin tells the display when the Raspberry Pi wants to talk to it, enabling communication only with the selected device.

Which Python library is typically used to communicate with SPI devices on Raspberry Pi?

A pygame

B spidev

C tkinter

D numpy

The spidev library provides an easy way to send and receive data over SPI on Raspberry Pi.

Why might the MISO wire be unused in SPI display modules?

A MISO is used for clock signals

B MISO is only for power supply

C MISO is replaced by CS pin

D Displays only receive data, they don't send data back

Most SPI displays only receive data from the Raspberry Pi and do not send data back, so MISO is often not connected.

What must you do before using SPI on Raspberry Pi?

A Enable SPI interface in Raspberry Pi settings

B Install a special display driver

C Connect the display to USB port

D Update the Raspberry Pi OS

SPI must be enabled in the Raspberry Pi configuration settings before it can be used.

Explain how SPI communication works between Raspberry Pi and a display module.

Think about how the Pi sends commands and data step by step.

Describe the steps to set up and use an SPI display module on Raspberry Pi using Python.

Start from turning on SPI to showing something on the screen.

Practice

1. What is the main purpose of using SPI with display modules on a Raspberry Pi?

easy

A. To power the display module

B. To connect the Raspberry Pi to the internet

C. To store files on the Raspberry Pi

D. To send commands and data quickly to the display

Solution

1. Step 1: Understand SPI role

   SPI is a communication protocol used to send data between devices quickly.

2. Step 2: Connect SPI to display modules

   On Raspberry Pi, SPI sends commands and data to control display modules efficiently.

3. Final Answer:

   To send commands and data quickly to the display -> Option D

4. Quick Check:

   SPI = fast data transfer to display [OK]

Hint: SPI is for fast data transfer to devices like displays [OK]

Common Mistakes:

• Confusing SPI with internet connection
• Thinking SPI stores files
• Assuming SPI powers devices

2. Which of the following is the correct way to open SPI bus 0, device 0 using the spidev library in Python?

easy

A. spi = spidev.SpiDev(); spi.open(0, 0)

B. spi = spidev.open(1, 0)

C. spi = spidev.open(0, 0)

D. spi = spidev.SpiDev.open(0, 0)

Solution

1. Step 1: Recall spidev usage

   spidev requires creating an SpiDev object first, then calling open(bus, device).

2. Step 2: Check syntax correctness

   spi = spidev.SpiDev(); spi.open(0, 0) correctly creates spi = spidev.SpiDev() then calls spi.open(0, 0).

3. Final Answer:

   spi = spidev.SpiDev(); spi.open(0, 0) -> Option A

4. Quick Check:

   spidev object then open() method [OK]

Hint: Create SpiDev object before calling open() [OK]

Common Mistakes:

• Calling spidev.open() directly without object
• Using wrong bus or device numbers
• Using incorrect method syntax

3. What will be the output of this Python code snippet using spidev?

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
response = spi.xfer2([0xAA, 0x55])
spi.close()
print(response)

medium

A. [170, 85]

B. Depends on the connected SPI device response

C. An error because xfer2 needs a string

D. [0, 0]

Solution

1. Step 1: Understand xfer2 function

   spi.xfer2 sends bytes and returns the response bytes from the SPI device.

2. Step 2: Recognize device dependency

   The returned list depends on the connected device's response, so output varies.

3. Final Answer:

   Depends on the connected SPI device response -> Option B

4. Quick Check:

   SPI response varies by device [OK]

Hint: SPI transfer output depends on device response [OK]

Common Mistakes:

• Assuming output equals input bytes
• Thinking xfer2 requires string input
• Expecting fixed output without device

4. You wrote this code to send a command to your SPI display but it raises an AttributeError:

import spidev
spi = spidev.open(0, 0)
spi.xfer2([0x01])
spi.close()

What is the error and how to fix it?

medium

A. spidev has no open() function; create SpiDev object first

B. xfer2() requires a string, not a list

C. spi.close() should be called before xfer2()

D. Bus number 0 is invalid on Raspberry Pi

Solution

1. Step 1: Identify AttributeError cause

   spidev module does not have open() function; open() is method of SpiDev object.

2. Step 2: Correct usage of spidev

   Create spi = spidev.SpiDev() first, then call spi.open(0, 0) to fix error.

3. Final Answer:

   spidev has no open() function; create SpiDev object first -> Option A

4. Quick Check:

   Use SpiDev() object before open() [OK]

Hint: Always create SpiDev() object before open() [OK]

Common Mistakes:

• Calling spidev.open() directly
• Passing wrong data type to xfer2()
• Closing SPI before transfer

5. You want to send a command byte 0xA5 followed by data bytes [0x01, 0x02, 0x03] to an SPI display using spidev. Which code correctly sends the command first, then the data, assuming spi is already opened?

hard

A. spi.writebytes([0xA5, 0x01, 0x02, 0x03])

B. spi.xfer2([0xA5, 0x01, 0x02, 0x03])

C. spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03])

D. spi.writebytes([0xA5]); spi.writebytes([0x01, 0x02, 0x03])

Solution

1. Step 1: Understand command and data separation

   Many SPI displays require sending command and data separately to distinguish them.

2. Step 2: Check code options

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) sends command byte first, then data bytes in separate calls, matching typical display protocol.

3. Final Answer:

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) -> Option C

4. Quick Check:

   Separate command and data transfers [OK]

Hint: Send command and data in separate SPI transfers [OK]

Common Mistakes:

• Sending command and data in one transfer
• Using writebytes() which may not return response
• Not separating command from data