Circuit Lake

Electronic Project and Circuit Collection

Expandable Serial Port Multiplexer

01/14/2010 Category: AVR, Digital, Interfacing, Microcontroller, Project

The Expandable Serial Port Multiplexer project allows a single RS232 serial port to service multiple instruments requiring RS232 ports. Each port is configurable in terms of baud rate, parity, number of bits and number of stop. On the host side the serial streams could be multiplexed through the use of a Windows driver or a special DLL program.


The Multiplexer uses a master processor (ATmega8) connected to a PC through a serial port. Multiple slaves (ATmega162) connect to master, via a parallel bus, to provide two serial ports each. Multiplexed commands sent to the master are routed to the appropriate slave. Likewise slave-received signals are routed back, through the master, to the PC in a multiplexed stream.

Gene Breniman, project designer, said that in addition to the slave serial port cards, other devices could be built and added to the stack to provide other services of interest to system integrators. Both A/D and D/A functional blocks could be added (based on the same ATMEL parts), to provide analog processing.

Serial Port Multiplexer
Download Project Documentation (zip)