Writing commands to I2C device in Raspberry Pi - Step-by-Step Execution

Concept Flow - Writing commands to I2C device

Start

↓

Open I2C bus

↓

Set device address

↓

Prepare command/data

↓

Write command to device

↓

Check for errors

↓

Close I2C bus

↓

End

This flow shows how a Raspberry Pi opens the I2C bus, sets the device address, writes a command, checks for errors, and closes the bus.

Execution Sample

Raspberry Pi

import smbus
bus = smbus.SMBus(1)
address = 0x20
bus.write_byte(address, 0xFF)
# smbus.SMBus object does not have a close() method
# so bus.close() is removed

This code opens I2C bus 1, writes the byte 0xFF to device at address 0x20.

Execution Table

Step	Action	Details	Result
1	Import smbus	Load I2C library	smbus module ready
2	Open I2C bus	bus = smbus.SMBus(1)	bus object created for bus 1
3	Set device address	address = 0x20	address stored as 32 decimal
4	Write byte	bus.write_byte(0x20, 0xFF)	0xFF sent to device at 0x20
5	End	No more commands	Program ends

💡 All commands executed successfully

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
bus	None	SMBus object for bus 1	SMBus object for bus 1	SMBus object for bus 1	SMBus object for bus 1
address	None	None	0x20 (32 decimal)	0x20 (32 decimal)	0x20 (32 decimal)

Key Moments - 3 Insights

Why do we need to open the I2C bus before writing?

The bus must be opened to create a communication channel; see Step 2 in execution_table where bus object is created before any write.

What happens if the device address is wrong?

The write command will fail or no device will respond; Step 4 shows writing to address 0x20, if incorrect, an error or no effect occurs.

Why close the bus after writing?

The smbus.SMBus object does not require explicit closing; resources are managed by the OS. Closing is not needed.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'address' after Step 3?

A None

B 0xFF

C 0x20 (32 decimal)

D SMBus object

💡 Hint

Check variable_tracker row for 'address' after Step 3

At which step is the byte 0xFF sent to the device?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at execution_table action column for 'Write byte'

If we forget to close the bus, what changes in the execution_table?

A No change at all

B Step 4 would fail

C Step 3 would change address

D Step 5 would be missing or different

💡 Hint

smbus.SMBus does not require closing, so no change

Concept Snapshot

Open I2C bus with smbus.SMBus(bus_number)
Set device address as hex (e.g., 0x20)
Write commands using write_byte(address, data)
No need to close bus explicitly
Always check for errors during write

Full Transcript

This example shows how to write commands to an I2C device using a Raspberry Pi. First, the smbus library is imported to access I2C functions. Then, the I2C bus 1 is opened by creating an SMBus object. The device address is set to 0x20. Using the write_byte method, the byte 0xFF is sent to the device at that address. The smbus.SMBus object does not require explicit closing; resources are managed by the OS. Each step is important: opening the bus creates the communication channel, setting the correct address targets the right device, and writing sends the command. If the address is wrong, the device won't respond. Forgetting to close the bus does not cause resource conflicts because closing is not needed. This step-by-step flow helps beginners see how commands are sent to I2C devices on Raspberry Pi.