Port Tags
Driver tags need to know where to find the hardware they will communicate with. Rather than build this information into the driver tag, VTScada provides Port tags, allowing you to define the communication details once, then use that configuration for several drivers. If the configuration changes later, then you need only update one tag.
Port tags tell the VTScada drivers about the nature of the physical connection (serial port, TCP/IP over Ethernet, or UDP) and the required configuration details such as IP address, port number, transmission speed, whether a modem is attached, etc.
Monitor drivers, not ports. A port tag has a value only on the server that is communicating with hardware and will be blank on all other servers. The value of a port tag is not synchronized across all workstations. (Unlike I/O and driver tags.) If the alarm server and I/O servers are different machines, an alarm on a port tag will not activate. Do not attach an alarm to any port tag.
A port tag widget drawn on a page represents only state of the port on the local machine.
Ports (TCP & UDP), Drivers, and Timing
A port will detect when a driver is using it. If the port is not used for a period of time defined by it’s “Disconnect Delay (sec)” parameter, it will close the connection to the PLC abruptly.
Drivers will always poll for PLC changes upon startup (including when the application starts and when the driver tag is re-started). This check will not initiate a connection if none is active.
The port's Disconnect Delay setting should always be greater than the driver's timeout setting (where the label and type of that timeout will vary by driver). The values that you choose will depend on the reliability of your network. In general, for longer polling cycles, of 5 seconds or more, it is best to close the connection between cycles by setting the driver's timeout and not by setting the port's Disconnect Delay.
Ethernet to Serial Converters - Troubleshooting.
