Once you have configured a Serial Card, you can set the serial port properties and add serial devices to the ports. The following table describes the configurable serial port properties.
Property |
Valid Values |
Description |
|---|---|---|
Baud rate |
300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, or 115200 |
Determines the baud rate for serial data exchange. |
Data bits |
7 or 8 |
Determines the number of data bits. Use 7 for ASCII and 8 for RTU mode. |
Description |
As many as 256 characters |
Describes the use of the port. This description only appears when you view the port properties from the DeltaV Explorer. |
Enabled |
Checked or not checked |
Enables the port. If the port is not enabled, the Serial Card does not scan for input data or transmit output when in master mode and does not respond to Modbus messages when in slave mode. |
Message timeout (ms) |
100 ms through 25.5 seconds in 100 ms increments |
Determines the amount of time the Serial Card waits for a response from the serial device after sending a request message. More specifically, this indicates the time from when the Serial Card sends the last character of the request message until the time the last character of the response message is received. This property is only applicable when in Modbus master mode. |
Mode |
Master or Slave |
Determines whether the port acts as a Modbus master or slave. |
Parity |
Even, Odd, None |
Determines the parity. |
Port type |
RS-232, RS-422/485 Full Duplex, RS-422/485 Half Duplex |
Determines the port type to be used for the serial connection. Note RS-485 Full Duplex is not supported when the card is configured as a Modbus slave in a multidrop configuration. |
Retry count |
0 through 255 |
Determines the number of times the Serial Card retries a failed message. This is only applicable when in master mode. When the Serial Card issues a Modbus request to a device, it expects a response message to be returned. If no response or an error response is returned, the Serial Card retries the failed message the number of times configured in the Retry count property. |
Send outputs on startup |
Checked or unchecked |
Determines whether the Serial Card sends all current output values to the serial devices on power-up, reset, switchover or after a download. This property is only applicable when in Modbus master mode. |
Stop bits |
1 or 2 |
Determines the stop bits. |
Transmit Delay (ms) |
100 ms through 25.5 seconds in 100 ms increments |
Determines the amount of time the Serial Card delays between requests for input data and/or requests to write output data to the Modbus Device. This value is used to slow down Modbus master requests being transmitted to slave devices that require a time delay between requests. The default Transmit Delay value is 0 since most Modbus devices do not require any delay. This value can also be used when in slave mode to delay the response to a Modbus master request. |