General description
The interface modules SERP28, XSP01L and XSP01R act as serial to parallel converters, to bring the status of eight input and eight output lines into a PC, a terminal or any other device with a serial RS232 port. Vice versa the eight output lines may be controlled by the serial device. As the inputs and outputs isolated by optocouplers the interface is best suited for harsh environment applications like industrial controllers. This interface module is not meant as a replacement for existing controller components, but rather as a supplement, if the number of digital inputs or outputs is not sufficient. Inputs and outputs are designed for 24VDC, common for most industrial controls. The XSP01-Series provides LEDs on the I/O-Lines, so the condition of each I/O can easily observed. While SERP28 and XSP01L components are equipped with semiconductor high-side switches, the XSP01R contains relays, allowing floating loads to 3A@250VAC or 3A@30VDC. The supply voltage for the internal logic circuits is also designed for 24VDC, though this little helper can operate without an additional power supply in most cases. The module can simply be mounted on a 35mm-DIN-Rail. Electrical connection for power and input/output lines is made by pluggable cageclamps.

The serial to parallel conversion is done by a PIC16F877. If the necessary equipment, for programming of the PIC16F877, already exists, the PIC16F877 can reprogrammed by the user, to realize special relations between the digital inputs and the digital outputs. The standard program reads the input and output lines on receipt of a serial command and returns the line status, or set the output lines according to the transferred parameters. In addition the input is scanned periodically (every 100ms) and compared against the last status. In case of any change, an unattended message will be send out, transferring the new line status.

As there is no need for any drivers, the communication with the module is a simple task, you have only set your communication parameters to 9600,8,N,1. The command string, that have to send to the serial RS232 port, is described below.