在Raspberry Pi，python smbus上使用I2C连续传输

Question

I want to transmit AVR or Arduino etc by I2C from Raspberry pi. I am writing in Python.

I already successeded communication using write_data() function in smbus module. But I want to transmit multiple bytes data consecutively.

Please tell me how to transmit multiple bytes data in i2c communication. I find write_block_data() function, but I don't understand the second parameter CMD . What is the CMD?? Should I specify the value of CMD ?

thank you.

Answer 1

Communicating between an RPi and an Arduino on I2C is a big mess if you are using Wire.h library. The short answer is that RPi is using a repetitive start signal while Arduino is not using it.

Repetitive start signal on I2C interface tells the slave to start answering for the call. In case of the Arduino asking and answering is in two separated calls. Therefore you cannot send block

I made two blog posts to interface the two architecture through I2C. First one is for using a remote controller PWM: http://distantorion.com/2014/10/24/rc-signals-pwm-to-i2c-with-arduino/ The second one is for driving a 128x64 LCD display on I2C: http://distantorion.com/2014/11/01/i2c-display-with-arduino/

In the second one I'm using block data in python:

bus.write_i2c_block_data(0x05,0x10,buff)

0x05 is the device address, 0x10 is the "command", buff containd the characters to display.

Regarding the commands. In I2C a slave works in a way of commands or registers. Both method looks like the same. If you are using a repetitive start signal the communication seems to be reading and writing registers. When you have no repetitive start signal, the communication looks like a command - answer system. In my example I'm sending 0x10 what is "put the characters from to the display". And 0x01 is a clear screen command, while 0x02 turns on the backlight.