RS232 Multiplexer in Low Cost Design

Figure 1 

The project illustrates aims to produce a multiplexer that would allow the connection of 4 devices to a single RS232 port.

The one single port can be used to control even an arbitrary number of devices through stacked multiplexers. One application is by connecting multiple stepper motor controllers to a single RS232 port where a simultaneous movement of all motors is made possible due to the simultaneous data reception mechanism. The design includes one master port and 4 slave ports making it function like a switch. The communication must be line based and each line must be terminated by a carriage return as the multiplexer works at a fixed data rate of 9600 baud.

An Atmel AVR AT90S2313-10 is used to power the multiplexer and the microcontroller program can be made available in two version including one for buffered receiving on all output ports and one for unbuffered switching only.

It is possible to stack multiple RS232 multiplexers where the master port of a multiplexer can be connected to the slave port of another multiplexer. Depending on the program version and signal running time, the maximum number of stacking levels may vary.

Rest of the project