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.
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by Seth Price