i use modbus poll for read data from soil Ph sensor I didn’t get any data and i set information by following the data sheet it’s always show timeout error

 

A Status Line Timeout error message in ModPoll means that a reply was not received in the expected time.

If you're polling at the one second default polling interval, that should be sufficient time for a reply, but you could increase the polling interval to 2 seconds which should be more than enough for any slave I've ever encountered to reply on a wired link (2 seconds could be to short for some wireless connections).

But the issue is most likely a comm link problem:


- serial comm settings must be identical on both ends
- wrong baud rate
- wrong word length (RTU = 8 bit, ASCII = 7 bit)
- wrong number of stop bits
- wrong parity selection on a serial connection
- polling message is addressing the wrong slave ID number or in TCP, the client is polling the wrong IP address for the server.
- serial connection wired incorrectly (some vendors label the RS-485 driver lines (A/B or +/-) backwards from other vendors. Try swapping the driver lines on one end to see if that's the case). No null modem wiring for RS-232.
- excessive electrical noise or common mode voltage corrupts either or both polling message or reply message (if bench testing, least likely cause): Missing signal ground, no shield/screen or miswired shield/screen in cabling, excess common mode needs a signal isolator.

 

A Status Line Timeout error message in ModPoll means that a reply was not received in the expected time.

If you're polling at the one second default polling interval, that should be sufficient time for a reply, but you could increase the polling interval to 2 seconds which should be more than enough for any slave I've ever encountered to reply on a wired link (2 seconds could be to short for some wireless connections).

But the issue is most likely a comm link problem:

View attachment 1796
- serial comm settings must be identical on both ends
- wrong baud rate
- wrong word length (RTU = 8 bit, ASCII = 7 bit)
- wrong number of stop bits
- wrong parity selection on a serial connection
- polling message is addressing the wrong slave ID number or in TCP, the client is polling the wrong IP address for the server.
- serial connection wired incorrectly (some vendors label the RS-485 driver lines (A/B or +/-) backwards from other vendors. Try swapping the driver lines on one end to see if that's the case). No null modem wiring for RS-232.
- excessive electrical noise or common mode voltage corrupts either or both polling message or reply message (if bench testing, least likely cause): Missing signal ground, no shield/screen or miswired shield/screen in cabling, excess common mode needs a signal isolator.

How about response error that's i tried by follow datasheet
and i check wiring ,baud rate,stop bit and length i thouht it's correct but when i change salve id to 0 it's show response error

 

The Slave address 0 is reserved for 'Modbus Broadcast mode' where all slaves internally comply with a Master command (if possible) but by Modbus Rules, no slave replies , because the network line would be jammed with multiple simultaneous replies. Function Code 03, which requires a reply with data, cannot be a function code for a broadcast command.

So your slave cannot be slave #0. You have to figure out what the default slave ID is and use the default ID # or figure out how to change the slave ID number to some other number. I am unaware of any vendor's default slave address being #0; which is not to say that some vendor can't do it, but it's highly unlikely.

Many slaves will not recognize a slave ID change (or other serial setting changes) until the power is cycled to the device.