Note: This article is intended for technicians which already familiar with basics of serial communication RS485
Polling software is requesting all devices via a communication master device by queue in the loop
and request-response to each device takes some time period.
Some device or segment in the loop might delay requests to all devices in the
1) Are there other devices in the loop where receiving response is delayed.
Are they located in same area?
2) Check response time for each separate device in PAS.
one of several problematic devices might delay requesting all other devices in the loop.
3) Check correctness of RS485 network installation.
Here are some requirements:
a) Should be used twisted pair cable. Shielded is recommended.
b) Communication cable must be installed separately from power supply of current
c) All devices must be connected by a chain one after another.
Star connection in not allowed.
d) Each segment of shield cable must connected only from one side to device port.
e) Should be installed termination resistors from both sided of the loop.
See illustration for example below.
General recommendation :In order to reduce total response time set 19200 or higher baud rate of all slave devices and the master port.