DTMF MT8870 with arduino for robot

Hi, I have attached my arduino to a MT8870 like in the following diagram: http://www.pablin.com.ar/electron/circuito/telefon/decdtmf/circuito.gif

Problem is that only one column of keys seems to work. This column changes from phone to phone- I have tested this with 2 phones. I have not installed any pull up/pull down resistors and nor is there any buffering b/w the outputs of the MT8870 and arduino, i.e. they are connected directly. Any plausible reason why this is not working? Thanks

code? actual schematic in use?


You should have resisters because the outputs go tri-state when no signal is present, I'd use the internal pullup ones. Buffers should not be required.

What have you got StD connected to? And post your code.