RS485 alarm if the other device does not respond in certain time

[admin]

You don't even need to store the time, you can simply count the number of times the device did not reply. Check the res variable contents because it will be nil on error and trying to manipulate res as a string will result in a script error.

Code:

res, err = port:read(27, 3) if res then   errors = 0   -- parse res contents else   errors = (errors or 0) + 1   if errors == 100 then     alert('device read timeout')   end end