Quad-port serial add-on for Ethernut


Ethernut 2 boards had one serial interface, mostly used for serial console I/O, in case networking was not (or net yet) available. In order to connect more serial devices, I developed an addon board which connected to the Ethernut 2 board thru its 50 pin connector. The board contained four MAX3100 interface chips, which talked to the Ethernut board via SPI protocol. 

A special device driver was developed which exposed the same API towards the applicatin programs as the standard serial driver. The device driver was interrupt driven to minimize CPU utilization. Serial transmission speeds of up to 230kbps were theoretically possible, but practical tests were limited to 38,4 kbps.