On Oct 26, 2012, at 4:22 PM, Tony Duell wrote:
One particular
scheme "evolved" due to the structured cabling being
shared between telephone and serial terminals - the serial stuff was
put on pairs not used by the phones, so as to reduce problems caused
by users plugging things into the wrong socket...
Avoid pins 4 and 5 for the serial port, that pair is commonly used for a
single telephone line.
Haiving ringing voltaeg (around 75-100V AC) appear between RS232 port
pins can really ruin your day.
A friend found out the hard way that you can't just hook up a PC sound
card to the phone line, either.
- Dave