Some customers use converters to transform communications. For example, RS-232 to TCP/IP or RS-232 to RS485 etc. MOXA is a popular manufacturer of such convertors. You may see a customer using our MatrikonOPC Server for MODBUS to connect to a serial device. If the serial device is a long way from the PC (RS232 is limited to about 20 meters MAX) that is running the OPC Server, the customer may use a MOXA convertor so that they can use ethernet (TCP/IP) up to the device and then convert to RS232 serial in order to interface with the device.
In this example, the MOXA converter is a networking device that maps an IP address to a COM port. It is used with lots of devices that can only speak serial but yet are needed to communicate over a TCP\IP network. In order to configure a MOXA from the same network you have to put the MOXA’s IP address on web browser which gets you to the MOXA web browser which allows you to configure it. Then on your local box you have to install a MOXA tool – found in OPCNAS0- to map a virtual COM port to the MOXA’s IP address.
Recently we were having lots of problems when trying to connect to a MOXA converter connected to an N2 device.
We found an option in the MOXA configuration that can cause issues if you are not aware of it. This option is called accessible IP settings and it is basically a list of IPs that the MOXA converter will allow to connect to it. If that option is unchecked then the MOXA converter will allow any IP to speak to it otherwise if that option is checked the MOXA converter will ONLY allow communication from the IP addresses listed in the accessible IP list. If that option is checked and your IP address is not in the list you will never be able to connect to it. So if you ever encounter an issue between an OPC server of ours and a MOXA device please consider the information provided here.
Contributed by: Mina Andrawos
Written by: Roger Fortune