How do you know what the address of the I2C device register is when using the writeRegister function?

Hello,

I have the following setup code. This connects an arduino and an I2C device (MCP23008).

a = arduino('/dev/tty.usbmodem1421','uno','Libraries','I2C');

dev = i2cdev(a,'0x20');

Now I am trying to figure out how to write data to control the device. I am trying the following:

writeRegister(dev, 32, uint8(bin2dec('10101010')))

I thought the register (32 above) would be the address property I get from dev.Address but nothing is happening on the board. Any ideas on how do I know what address I need to target or is the data that I am trying to send actually incorrect?

Answer 1

[Walter Roberson]

The 23008 is an 8 bit I2C interface.

The 0x20 is the port number on the arduino. dev.Address is returning that in decimal form (32). However when you write a register you need to send the register number. Which register number you should send depends what you are trying to do.

See http://ww1.microchip.com/downloads/en/AppNotes/01043a.pdf for a list of register names and addresses, and note that you need to use the left half (8 bit) of that diagram only.