Accessing devices with Slave-ID 0 is impossible

[alphafalcon]

If I try to run
modbus 192.168.X.Y:502 -s 0 REGISTER
I get a TimeoutError. Sniffing with wireshark revealed that modbus-cli was sending a slave-id of 255.
I belive that this line is responsible, as 0 is interpreted als falsy and gets replaced by 255.

modbus-cli/modbus_cli/modbus_tcp.py

Line 12 in dbe8939

if not slave_id:

A possible fix would be adding a default of 255 to the command line argument -s and dropping the check referenced above. This should not change the behaviour, unless 0 is explicitly set on the commandline

[favalex]

Hi, thanks for your report. Do you have a chance to see if #38 solves your problem?

[alphafalcon]

Yes, i can now send messages with unitid 0 using the linked branch, thanks!