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ring indicator over a serial port

R

Rob

Jan 1, 1970
0
i need to fake a ring indicator signal over a db9 serial port. i think its
just a matter of applying voltage to a couple of pins. before i go randomly
playing, does anyone have any idea of the specifics? thanks!
 
R

Rob

Jan 1, 1970
0
i figured it out, in case anyone ever searches google for this, its 5 and 9
 
Q

Quack

Jan 1, 1970
0
I am pretty sure the voltages are not the same.
Either it wont do anything, or you may damage your comport, i'd google
around and look at dtmf circuits etc to see how to interface to a
phone line before playing around ...

(i think i remember something about -50v supply for phones - i have
been in a few t.exchanges and they have huge power thingies, all
generating -50v)

good luck :)
 
Q

Quack

Jan 1, 1970
0
It just occured to me that you are probably NOT trying to fake a ring
on a telephone - but are trying to fake a ring indicator from a modem
?

So you want to 'pretend to be a modem' and give out an RI signal ?

Okay connect GND and RI to the remote end, from your com port to the
com port you want to talk to.

pins on your db9;
gnd=5
ri=9

Now in your software, you want to write a '1' to the right place, so
your RI pin goes 'high', and the other end should get it.

base=the commport address, eg: 0x3f8 is normal for COM1, 0x2f8 is
normal for COM2.

base+6 = MSR (modem status register)
In this register, you want to play with the top 4 bites, which are;
DCD RI DSR CTS - - - -

so write %01000000 or 64 to 3FE (if you have a normal address and are
using COM1).

Never tried it, seems like it should work.

The other problem is from what i remember of working with modems, they
also tend to say "RING" in ascii when they get a call, you might want
to fake that too, depending on what your trying to fool, it may need
it.
 
G

Garrett Mace

Jan 1, 1970
0
Quack said:
I am pretty sure the voltages are not the same.
Either it wont do anything, or you may damage your comport, i'd google
around and look at dtmf circuits etc to see how to interface to a
phone line before playing around ...

(i think i remember something about -50v supply for phones - i have
been in a few t.exchanges and they have huge power thingies, all
generating -50v)

good luck :)


He was trying to fake the signals that an external modem sends to a computer
through an RS232 port in order to indicate an incoming call. Not, in fact,
trying to generate ring voltage for a telephone line.
 
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