libmodbus trouble with reading from slave
Strange that it uses 9600bps... most of the modbus devices I've seen use 19200 bps. Could you test it with the MODPOLL tool to see if you can communicate with it, and if/when you do, post the parameters that proved to be working.

As you probably know, there's two basic modbus protocols, MODBUS/ASCII and MODBUS/RTU. I didn't find from the datasheet which one it is using, so maybe you're using the other one. If it's using 9600bps, then it might very well be MODBUS/ASCII.