Writing pins to the RS232

[Nick Craig-Wood]

Richard Brodie <R.Brodie at rl.ac.uk> wrote:
>  If you just need one or two signals, then it might be practical to use one
>  of the control lines, and PySerial supports this (UPS monitoring software
>  often works this way).

I've done this many times (not with PySerial) for misc sensors.

With PySerial you can read 4 pins (ie 4 inputs)

  getCD(self)
      Read terminal status line: Carrier Detect
  
  getCTS(self)
      Read terminal status line: Clear To Send
  
  getDSR(self)
      Read terminal status line: Data Set Ready
  
  getRI(self)
      Read terminal status line: Ring Indicator

and set two outputs

  setDTR(self, on=1)
      Set terminal status line: Data Terminal Ready
  
  setRTS(self, on=1)
      Set terminal status line: Request To Send

Other than those 6 that you have Rx, Tx and Ground which you can't use
for logic, on a standard 9-way PC serial port.

You need to set the serial port up not to do automatic handshaking
first (eg setDsrDtr() & setRtsCts())

RS232 levels are +/- 12V, though a lot of computers only generate +/-
5V.  The threshold is +/- 3V IIRC.

-- 
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick