Serial hacking with an ATtiny2313
posted Aug 6th 2009 6:14am by Steve Watkinsfiled under: home entertainment hacks, misc hacks, pcs hacks
[Sprite_tm] automated a portion of serial hacking by sniffing out the baud rate using an ATtiny2313 and FT232 breakout board. The firmware assumes 8 data bits, no parity, and 1 stop bit (8N1). This is pretty much defacto among serial ports so it should work well, though some devices do use different settings. The auto detection routine can sniff rates as low as 110 baud and supports non standard rates. Released under GPLv3, the software is also supplied in hex format. [Sprite_tm] has provided great project in past such as Working with VFDs, Controllable bristlebot, and AVR boost converter. Additional information regarding serial hacking after the break.
A great deal of electronics have an Achilles’ heel, known as a serial port. These embedded ports are often used during development to debug functions, load and upgrade firmware etc. At the very least circuit traces are generally brought out for automated testing purposes. Looking up chip pin outs and tracing circuits is one small step in serial hacking. After the traces are known the voltage level is then determined(CMOS,TTL,RS232,etc). Then a few tests are run on the port. These tests generally give indications regarding the potential of the port(does it have a driver, does it have a protocol, what is the baud, etc). If information regarding the baud and other criteria can not be found in the data sheet, [Sprite_tm]‘s method would certainly save a great deal of tedious time. Some controllers, like the 68HCxx may have a boot ROM which eliminates most of the guess work in setting up the serial port. We use the Null-modem emulator project (com0com) almost daily to help sort various serial problems. This is highly recommended, for anyone spending a considerable amount of time with serial devices.
This would be a great feature to add to the Bus Pirate.