On 14 Jun 2012 at 17:30, Dave McGuire wrote:
    Just to jump in...I don't know about machines,
but at least one of
   the
 later MAX232 family chips can be configured to do this.  It's a
 power-saving measure; it shuts down the charge pump.  Note that this
 is not the "MAX232", but one of that family, which comprises upwards
 of thirty completely different chips now. 
Linear Technology EIA transceivers ; e.g. LT1080--pretty much have
always had that feature--with an ON/OFF pin.
--Chuck