# Defining an RS-232 Serial Port

## Introduction

The RS-232 MWI application allows servers to turn PBX message waiting indicators on and off by sending signals to the PBX over RS-232 data links. The data links can be either direct serial connections to the PBX, or they can connect to modems that are connected to analog ports on the PBX.

When a message is left in a mailbox, the server sends an ASCII message that tells the PBX to turn on the message waiting indicator at the appropriate station. Conversely, when all unplayed messages are played, the server sends an ASCII string that directs the PBX to turn off the message waiting indicator.

## Requirements

To use any of the RS-232 message waiting indicator interfaces, an RS-232 cable must be run from a server serial port to the PBX (or, in the case of Centrex RS-232 MWI interface, to a modem that communicates with the Central Office).

The physical setup uses RS-232 pins 2, 3, and 4, with communications parameters of 1200 baud, 8 data bits, 1 stop bit, no parity, full duplex, and no flow control.

If you have an expansion serial port card installed in your server, you can use as many serial ports as necessary for the programmable RS-232 message waiting application. You must first assign and configure a single serial port using index 1, which enables any additional ports assigned to the application to adopt the configuration of the first port.