[SOLVED] i2cdetect command does not locate attached MCP23017 port expander

Hi:

I am attempting to get a Raspberry Pi to communicate with a MCP23017 port expander via the I2C interface. The address pins
A0, A1 & A2 on the expander are all hard wired to 0. When I executed the i2cdetect command the response was:

$ sudo i2cdetect -l
i2c-1 i2c bcm2708_i2c.1 I2C adapter

I then ran the same command with i2cbus set to 1 and again with it set to abcm2708_i2c.1 and received the following response both time:

pi@raspberrypi ~ $ sudo i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- UU -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

According to the documentation I have the output should be:

0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Finally I ran the command with the F option with -F 1 and again with -F bcm2708_i2c.1 and it seemed to work OK although I would have expected it to fail also.


Does anybody have an idea as to why I'm NOT seeing the "20"?
Also the man page says that the "UU" indicates probing was skipped because this address is currently in use by a driver. Since this not the address I'm interested in should I be concerned about the"UU"?


Thanks

Jerry

As far as I know the output of -F displays information about the adapter on the Pi not what is attached to the bus. Do you have any other i2c software etc running? I would be a little curious since your device is not being detected at the desired address.

By 0 I assume you mean ground. Are all the ground pins tied together? What are you using for VDD i.e. 3 or 5 VDC and where are you getting the power from? Did you connect pin 18 (reset) to VDD?

Originally Posted by michaelk As far as I know the output of -F displays information about the adapter on the Pi not what is attached to the bus. Do you have any other i2c software etc running? I would be a little curious since your device is not being detected at the desired address. By 0 I assume you mean ground. Are all the ground pins tied together? What are you using for VDD i.e. 3 or 5 VDC and where are you getting the power from? Did you connect pin 18 (reset) to VDD?

Michael:

I read your reply and then realized that although I had tied together the grounds on the power supplies and the MCP23017 boards
I had failed to connect them to the Raspberry Pi ground. When I did this the i2cdetect showed the correct X20 address.


Thank You so much for your help

Jerry

Glad you got it working. You can mark the thread as solved via the thread tools pull down menu at the top of the page.