Insufficient data received error in modbus

[paddy]

Hi,

I have a monitor which is programmed as modbus slave (RTU).

When I am connecting single device and checking the RS485 communication using Modbus poll and RS232 to RS 485 converter, it works fine. But when I connect another similar device in loop at that time it gives insufficient data byte error and CRC error.

For single device there is no problem but it gives error when I add another device. Please find attached text file.

Please advice what could be the problem.

Thanks,
Paddy

 

[paddy]

Hi,
The problem was occurring because of improper voltage (reverse voltage i.e. VCC is connected to GND and vice versa) to bias resistors.

Regards,
Paddy

 

[KrisBlueNZ]

Thanks for following up here.

So that error meant that when a device stopped driving the RS-485 bus, it would be pulled into a break state? And that causes the Master to report "insufficient data" and a CRC error?