Chap 5 - Serial is garbled

[hexagon5un]

Chap 5 - Serial is garbled

[hexagon5un]

Great that you're having a good time with it!

There's "serial" and there's "serial" -- what we need is a TTL (3.3V or 5V) serial adapter rather than an RS-232-style adapter. If you've got an RS-232 adapter (or are just using a computer's serial port) that could explain it?

In brief: RS-232 uses +12V/-12V signal levels rather than 0V/5V, and what's worse the low voltage in RS232 stands for a 1 bit, while in TTL serial, the high voltage is a 1. So to convert, you need to get the voltage levels right and invert the logical sense of things.

If you've already ordered an FTDI TTL serial cable, you should probably just sit tight. That's the elegant solution anyway.

If you're looking to build a simple level-conversion circuit, you can try one of these:
http://freecircuitdiagram.com/2009/03/27/simple-ttl-rs232-level-converter-using-transistor/
It's basically just two transistors to do the logic inversion and level shifting. I made one of these fifteen years(!) ago when I was just starting learning about microcontrollers and all I had was a serial port on an old desktop computer.

Thanks for the question. I'll try to work an update clarifying this into the next version of the book, if they let me get away with the extra couple paragraphs.

Let me know if the FTDI cable clears things up.

  Elliot.

[jonmiller1]

I just received the FTDI USB to TTL Serial cable (3.3V) Part No TTL-232R-3V3. It totally solved the problem and everything works great! Thanks again for your fast response and for your awesome book! I love that you are continuing to revise and refine it. I found a good article that explains the difference. I had no idea that RS-232 serial on PCs was different than Serial on micro-controller. Thanks!

https://www.sparkfun.com/tutorials/215