SPI library usage in Arduino - Step-by-Step Execution

Concept Flow - SPI library usage

Include SPI library

↓

Initialize SPI settings

↓

Begin SPI communication

↓

Send/Receive data

↓

End SPI communication

This flow shows how to include the SPI library, set it up, start communication, transfer data, and then end communication.

Execution Sample

Arduino

  #include <SPI.h>

  void setup() {
    SPI.begin();
    SPI.beginTransaction(SPISettings(4000000, MSBFIRST, SPI_MODE0));
  }

  void loop() {
    byte response = SPI.transfer(0x42);
  }

This code initializes SPI, starts a transaction with specific settings, and sends a byte while receiving a response.

Execution Table

Step	Action	SPI State	Data Sent	Data Received
1	Include SPI library	Not started	N/A	N/A
2	Call SPI.begin()	SPI initialized	N/A	N/A
3	Call SPI.beginTransaction(4MHz, MSBFIRST, SPI_MODE0)	Transaction started	N/A	N/A
4	Call SPI.transfer(0x42)	Transaction active	0x42	0x00 (dummy)
5	Loop repeats SPI.transfer if called again	Transaction active	0x42	0x00 (dummy)

💡 SPI communication continues until program stops or SPI.endTransaction() is called

Variable Tracker

Variable	Start	After SPI.begin()	After SPI.beginTransaction()	After SPI.transfer()
SPI State	Not started	Initialized	Transaction active	Transaction active
Data Sent	N/A	N/A	N/A	0x42
Data Received	N/A	N/A	N/A	0x00 (dummy)

Key Moments - 3 Insights

Why do we call SPI.begin() before transferring data?

SPI.begin() sets up the hardware SPI pins and prepares the SPI bus; without it, SPI.transfer() won't work properly as shown in step 2 of the execution_table.

What does SPI.beginTransaction() do?

It sets the SPI speed, bit order, and mode for communication, ensuring devices talk correctly; see step 3 where transaction starts with specific settings.

Why does SPI.transfer() return a value?

SPI is full-duplex, so while sending data, it simultaneously receives data from the slave device; step 4 shows sending 0x42 and receiving 0x00 (dummy data).

Visual Quiz - 3 Questions

Look at the execution_table, what is the SPI state after calling SPI.begin()?

A Not started

B Transaction active

C Initialized

D Ended

💡 Hint

Check the SPI State column at step 2 in the execution_table

At which step does the SPI transaction start with specific settings?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look for 'Transaction started' in the SPI State column in execution_table

If SPI.beginTransaction() was not called, what would likely happen when SPI.transfer() is called?

A Data would send and receive normally

B SPI.transfer() would fail or use default settings

C SPI bus would reset automatically

D SPI.transfer() would send zero bytes

💡 Hint

Refer to key_moments about the role of SPI.beginTransaction() and step 3 in execution_table

Concept Snapshot

SPI library usage in Arduino:
- Include <SPI.h>
- Call SPI.begin() to initialize SPI pins
- Use SPI.beginTransaction(SPISettings) to set speed, bit order, mode
- Use SPI.transfer(byte) to send and receive data
- End with SPI.endTransaction() when done

Full Transcript

This visual execution shows how to use the Arduino SPI library step-by-step. First, the SPI library is included. Then SPI.begin() initializes the SPI hardware pins. Next, SPI.beginTransaction() sets communication speed, bit order, and mode. After that, SPI.transfer() sends a byte and simultaneously receives a byte from the slave device. The SPI state and data sent/received are tracked at each step. Key moments explain why initialization and transactions are needed and why SPI.transfer returns data. The quiz tests understanding of SPI states and transaction steps. The snapshot summarizes the main SPI usage steps in Arduino.