The RS485 port is used for data communication with standard Modbus RTU devices.

Client mode

In Client mode, right-click on an RS485 port to configure the RS485 parameters of the controller on the Device Configurator page. See the following table for details:

Parameter

Description

BaudRate

Communication rate

TransFmt(Start-WordLength-Parity-Stop)

Data transfer format

EnbTermRes

Enables or disables line resistance

ResponseTimeout(ms)

  • The longest reaction time that Server responds to the request of Client. Parameter adjustable.
  • The timeout of the controller depends on the maximum timeout of the sub-device that acknowledges frames slowest in the RS485 bus network. The controller resends a read/write request after each timeout. It resends max. three times.
  • When acting as Client, the controller allows connection of up to 31 Server devices with different physical addresses. A Server device is determined to be offline if it times out four times in a row. The cycle read and write process skips all its configurations to improve the efficiency of bus data communication.
  • For a Server device that has been determined to be offline, the controller sends the first read/write request of its configuration information every 30 seconds. If the sub-device acknowledges the request, the controller determines that it is online again. Cycle reads and writes then begin to perform all its configuration information. If the timeout persists, the controller repeats the request every 30 seconds until the Server device is online again.
  • When acting as Modbus TCP Server, the controller can connect to max. four Modbus TCP Client devices. The timeout of the Modbus TCP Client end timeout is typically set to 1000ms, which can cover most data traffic situations. If there are too many data points under "Communication Configuration" > "Server Points", the Client should set a longer timeout accordingly.

UpdateTimerT1(ms)

  • Polling timer periods of the Modbus Data Acquisition. Parameter adjustable.
  • The T1 value must be less than the T2 value. T1 value range: 100...5000 ms; T2 value range: 1...255 s.
  • Set an acquisition cycle to ensure that all read and write configurations under "Communication Configuration" > "Client Points" can be executed within the cycle. In general, 10 data packages can be sent every one second at a baud rate of 9600 bps, when there is no offline Server device, high resource consumption or other timeout-generated events.
    The specific settings for the acquisition period can be determined based on the number of configured acquisitions. At the same time, the variable triggers a write request every time a "COV (Change of Value)" is generated.
    Note: COV refers to value change of a communication variable of Client.

UpdateTimerT2(s)

HeartbeatTimerH1(s)

  • The data point value is delivered based on the configured heartbeat cycle value. Parameter adjustable.
  • The H1 value must be less than the H2 value. Both values range from 10 seconds to 18 hours.

HeartbeatTimerH2(s)

Note:

  • When the controller is Client, Server devices must be added and configured. See "Add and configure sub-devices" for details.
  • The controller uses a cyclic read/write or COV-triggered write command communication method. The cyclic read/write executes configurations under "Communication Configuration" > "Client Points" one by one. The COV-triggered write command executes immediately a corresponding request configured in "Client Points" if a communication variable changes to another value in the program.

Server mode

In Server mode, right-click on an RS485 port to configure the RS485 parameters of the controller on the Device Configurator page. See the following table for details:

Parameter

Description

BaudRate

Communication rate

TransFmt(Start-WordLength-Parity-Stop)

Data transfer format

EnbTermRes

Enables or disables line resistance

Server Address

Communication address of the Server

NOTICE

The timeout for the Client device to wait for the ELC controller to reply frames depends on the communication baud rate and the contents of the transmitted frame. In general, normal communication is guaranteed at a baud rate of 9600 bps and a timeout of 1000 ms. If there are too many data points under "Communication Configuration" > "Server Points", the Client should set a longer timeout accordingly.