Wire library for I2C in Arduino - Step-by-Step Execution

Concept Flow - Wire library for I2C

Start

↓

Initialize Wire

↓

Begin Transmission

↓

Send Data

↓

End Transmission

↓

Request Data

↓

Read Data

↓

Stop

This flow shows how the Wire library starts, sends data, requests data, reads it, and stops communication on the I2C bus.

Execution Sample

Arduino

Wire.begin();
Wire.beginTransmission(8);
Wire.write(42);
Wire.endTransmission();
Wire.requestFrom(8, 1);
int x = Wire.read();

This code initializes I2C, sends the number 42 to device 8, then requests and reads one byte from device 8.

Execution Table

Step	Action	Wire Function	Data Sent/Received	Result
1	Initialize I2C bus	Wire.begin()	None	I2C bus ready
2	Start sending to device 8	Wire.beginTransmission(8)	None	Transmission started
3	Write byte 42	Wire.write(42)	42	Byte queued to send
4	End transmission	Wire.endTransmission()	42 sent	Data sent to device 8
5	Request 1 byte from device 8	Wire.requestFrom(8, 1)	Request sent	Waiting for data
6	Read received byte	Wire.read()	Received byte	Byte stored in variable x
7	End	None	None	Communication complete

💡 All steps complete, data sent and received successfully

Variable Tracker

Variable	Start	After Step 6	Final
x	undefined	Received byte from device 8	Received byte from device 8

Key Moments - 3 Insights

Why do we call Wire.beginTransmission() before Wire.write()?

Wire.beginTransmission() tells the I2C bus which device we want to talk to. Without it, Wire.write() wouldn't know where to send data. See step 2 and 3 in the execution_table.

What happens if we call Wire.read() before Wire.requestFrom()?

Wire.read() reads data from the buffer. If we don't request data first, the buffer is empty, so we get no useful data. See step 5 and 6 in the execution_table.

Why do we call Wire.endTransmission() after Wire.write()?

Wire.endTransmission() actually sends the queued data to the device. Wire.write() only queues it. See step 3 and 4 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what function is called to start sending data to device 8?

A Wire.write(42)

B Wire.beginTransmission(8)

C Wire.requestFrom(8, 1)

D Wire.endTransmission()

💡 Hint

Check step 2 in the execution_table where transmission starts.

At which step is the data actually sent to the device?

A Step 3

B Step 5

C Step 4

D Step 6

💡 Hint

Look at the action 'End transmission' in step 4.

If we want to read 2 bytes instead of 1, which function call changes?

A Wire.requestFrom(8, 2)

B Wire.write(42)

C Wire.beginTransmission(8)

D Wire.endTransmission()

💡 Hint

Check step 5 where data is requested from the device.

Concept Snapshot

Wire library manages I2C communication.
Use Wire.begin() to start.
Wire.beginTransmission(address) sets device.
Wire.write(data) queues bytes to send.
Wire.endTransmission() sends data.
Wire.requestFrom(address, count) asks for bytes.
Wire.read() reads received bytes.

Full Transcript

The Wire library helps Arduino talk to devices using I2C. First, we start the bus with Wire.begin(). To send data, we tell which device with Wire.beginTransmission(address), then queue data with Wire.write(), and finally send it with Wire.endTransmission(). To get data, we ask with Wire.requestFrom(address, number_of_bytes) and read it with Wire.read(). This step-by-step flow ensures data goes to and comes from the right device.