The communication functions give you direct access to the communication ports on your computer(s). You can use these functions to communicate with external equipment, such as low speed devices (e.g. bar code readers), serial keyboards, and dumb terminals.
You should not use these functions to communicate with high speed PLCs, as they are designed for low-level communication on a COM port and the performance may not be adequate. To communicate with a PLC, a standard I/O device setup should be configured using the required driver.
Note: The Communication functions can only be called from an I/O server.