3 Jun
2009
3 Jun
'09
11:41 a.m.
On Wed, Jun 3, 2009 at 11:37 AM, Dave McGuire <mcguire at neurotica.com> wrote=
:
Formally, yes, that's the max signalling voltage, but in practice,
I thoght that one state was a positive voltage between +3V and +25V wrt
signal ground and the other state was a negative voltage between -3V and
-25V wrt signal ground. Anything between -3V and +3V is illegal.
There's no requiremnt, AFAIK, for the 2 votlages to be of the same
magnitude. A signal which swings between +12V and -5V is perfectly valid.
This explains a little circuit that I've sene used in small RS232
peripherals that run off their own wall-wart. Namely to use a 7905 (-5V)
regulator to power the logic. The common +ve raill (wall wart +ve,
regulator common pin) is the +5V line, the regulator output is the logic
ground (so there's the normal 5V supply, right way round, for the logic).
The RS232 driver is a discrete transsitor circuit running between the +5V
line and the (unregulated) input to the regulator -- the -ve side of the
wall-wart. Provided the latter is large enough, this does meet the RS232
spec.
-tony
On Jun 3, 2009, at 12:06 AM, Jay West wrote:
>
> These devices had a lot of trouble with RS423, where the voltage was muc=
h
> less than RS232. I don't recall the exact
numbers but RS232 was somethin=
g
about 12V
swings
=A0+/- 15V