Board with RS232 communication

Comments

• Peter Jakacki Posts: 10,193

  2012-06-29 06:34 edited 2012-06-29 06:34

  Unfortunately I deal with RS232 continually but you don't *need* an RS-232 port or a DB9 for that matter on a board. May I suggest that you use two resistors and a 3-pin header that an "RS-232" cable can plug into. If you use 100K from the TXD of the external device to the Prop RXD line and just for insurance against shorts use a 220R or there-abouts from the Prop's TXD to the external device's RXD. Just set the mode in your serial coms to 3 rather than 0 to invert the signals. That is: coms.start(rxpin,txpin,3,9600) for instance. Just ignore any muttering you hear about how it's not "proper" RS-232 and just do it. Unless you are running many many meters or more it will never be a problem. The 100K limits the current into the Prop's pin very effectively and there is no need to use any other clamping although if you want to disconnect the external device you should have a pull-down on the input to prevent the Prop's pin from floating. The TXD from the Prop will "only" be 0 to 3.3V but all that the RS-232 receiver in the external device is worried about is anything above 1.7V or so or anything below 1.2V or so, that's it, guaranteed.
  
  

  RS-232 RXD <--------------220R-----------< PROP TXD
  RS-232 TXD >------|--------100K----------> PROP RXD
                   10K
                    |
                   GND
  
• msrobots Posts: 3,709

  2012-06-30 03:42 edited 2012-06-30 03:42

  well there is the Propeller Professional Development Board from parallax having a Max232 aka RS232
  and that black one (RPM?) also
  
  Enjoy!
  
  Mike