Sierra Wireless DART 300 Sample UDP/TCP Configurations, Case 1 Semi-intelligent RTU, Cabling

User’s Guide UDP/TCP Service

8.4. Sample UDP/TCP Configurations

8.4.1.

These are actual sample cases. They are provided as a guideline to aid your configuration planning.

Case 1 – Semi-intelligent RTU

The host device is a Remote Terminal Unit (RTU) designed for industrial control and monitoring applications.

It provides an ASCII user interface, terminating lines with <LF><CR>. The unit can accept single characters as commands; responding to unrecognized characters with a single prompt line showing the valid command characters. The device cannot issue AT commands, and cannot process modem result codes. The messages from the device do not contain the characters “AT” in sequence so its messages will not be processed by the modem’s command state processor.

The device will generate a message whenever an input value changes. These messages are unsolicited status reports. The device can also issue status reports on request.

This situation suggests that the device should be configured as a UDP server, without a session timeout, and with the Server Receive Lock enabled. The device will remain in an open session, sending unsolicited status to the last calling client. The Server Receive Lock allows the user to change monitoring systems (clients) if needed, or to call the device from multiple systems.

Other configurations are possible, including closed sessions, since the unsolicited messages from the RTU are harmless to the modem’s command processor.

Cabling

The RTU is configured as DTE meaning that it is designed to connect directly to a modem. However, the unit does not support bi-directional flow control using RTS/CTS. It uses the outmoded application of RTS, only asserting RTS when it wants to transmit. The DART 300 will not send the device any data unless RTS is active; an indication to the DART that the local host is ready to receive. The RTU can operate using only Rx, Tx, and GND.

To use the RTU with the DART 300, the DART must see asserted RTS and DTR signals. This cable will assert both of these.

The cable’s DCE end has a male connector and plugs into the modem. The DTE end has a female connector on the cable and plugs into the RTU.

DCE (male)

1DCD

2RxD

3TxD

4DTR

5GND

6DSR

7RTS

8CTS

9RI

Not Connected

Not Connected Not Connected

DTE (female)

1DCD

2RxD

3TxD

4DTR

5GND

6DSR

7RTS

8CTS

9RI

Figure 8-1: Cable Without DTE-DCE Flow Control.

Rx, Tx, and GND are straight through (DTE to DCE). The modem’s DSR is tied back to RTS and DTR to assert these two control signals that RTU does not provide.

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