Servo - May 2011

A UART/SPI Monitor For Your Micro

by Mark Mitchell

Probably the most important thing when trying to debug robot problems or any microcontroller based systems is VISIBILITY! If you can’t see it you, can’t fix it.

The objective of this project was to create a tool to increase visibility into the operation of a microcontroller — and ultimately a robot — by getting access through either the serial port or the SPI port, both of which are pretty ubiquitous fixtures on most micros.

www.servomagazine.com/index.php?/magazine/article/may2011_Mitchell

Iam sure all microcontroller programmers have used some sort of print statement out a serial port to see what is going on at one time or another. Before in-circuit emulators were available, it was pretty much the main way of debugging. The SPI port is another place that one would like to know what is happening, especially when things are not working properly (which always seems to be at the most inconvenient time).

To gain better visibility into both of these ports (and because I was tired of digging around for that serial to RS-

232 board for the thousandth time), I decided to build a tool that could be used on a standard UART to provide the tried and true debug printing to a PC. It would also display the SPI data out (DO) line activity and could inject an SPI data stream to provide a known good data stream for SPI data in (DI) exercising. The SPI monitor also allows me to avoid having to hook up and decode the SPI signals on an oscilloscope — a tool which may not always be available.

Since this project was pretty small, I decided to build it using the BoardworX universal prototyping system which

FIGURE 1. Schematic for the

SPI/UART monitor.

A complete kit to go with this article can be purchased online from the SERVO Webstore at www.servomagazine.com or call our order desk at 800-783-4624.