Lynn's Industrial Protocols over IP

Thursday, January 11, 2007

WiFi 802.11b Modbus Bridge - TCP to serial

- Want to query a movable Modbus slave on a conveyor?
- Want to roll a Modbus Master HMI around on a cart or AGV?
- Want to query your outdoor oxygen tanks without running a cable through the wall?

I was a bit surprised, yet pleased, to see our embedded team selected to port the Modbus Bridge function into the full line of low-end Digi Connect products. The latest 82001220_H2.bin firmware for the small, low-cost Digi Connect Wi-SP includes Digi's basic Modbus bridge functionality which allows network Modbus masters to share serial Modbus RTU and Modbus ASCII slaves. It is similar to the function of the Digi One IA and a subset of the Digi One IAP.

Protocol and transport combinations supported:
  • Modbus/TCP
  • Modbus/TCP via UDP/IP
  • Modbus/RTU via serial, TCP/IP or UDP/IP
  • Modbus/ASCII via serial, TCP/IP or UDP/IP

So for example, a Modbus/TCP OPC server could query a portable Modbus/RTU serial slave; such as a machine cell moved around as production mixes require. Or a serial Modbus/RTU master on a repair cart could wirelessly query network-based Modbus PLC and test devices.

Here is the full datasheet for the Digi Connect Wi-SP, but feature summary:

  • Field selectable RS-232, RS-422, RS-485
  • Flexible 9-30vdc power supply (serial NOT isolated from power ground)
  • Standard 802.11b with WPA2/802.11i security
  • SSL/TLS strong security support
  • Digi RealPort support for comm-port redirection
  • Software development tools available for custom firmware development

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