3 Jun
2009
3 Jun
'09
11:30 a.m.
It was written...
Was it? I can't think of many classic RS232 devices that have those pins
wired.
Huh? The RS-232-port isn't supposed to
deliver any power at all.
Not quite true, but a case can be made.... As per the
spec, pins 9 and 10
are reserved specifically to provide test voltages. The current available is
minimal and designed mainly for testing purposes with breakout boxes, etc.
But it is there (from those that chose to implement it - which back in the
day was most folks). Not only that, but it was not uncommon - in fact very But I'd be
surprised if a circa-70s modem was ever designed to use the
power from the RS-232 port to drive the modem itself. I'd expect it to
have an external power supply.
I can't imagine a 70's era modem getting
power from the interface. Well, not
a modem designed to interface to analog POTS lines. A line driver or short
haul modem? Heck yeah, I've seen scads of them that got their power from the
RS232 interface.