bare minimum serial cable

[C3]

I want to quickly build a serial cable to connect a modem to my serial port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?


C3

 

[MC]

C3 wrote:

I want to quickly build a serial cable to connect a modem to my serial port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?

Definitely include the Ground.

The modem *might* want DTR asserted. (depends on how you've configured it)

It usually doesn't hurt if you connect RTS to CTS at each end.


This should work if you have 9-pin connectors at each end.

2 ---- 2
3 ---- 3

5 ---- 5

4 \ /4
6 / \6

7 \ /7
8 / \8

If you have a 25-pin at one end and a 9-pin at the
other you'll need to (at least) swap pins 2 & 3.

 

[Leon.]

"C3" <user@host> wrote in message
news:3fd66b05$0$1020$afc38c87@news.optusnet.com.au...

I want to quickly build a serial cable to connect a modem to my serial
port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX.

And ground.

Are all the other signals
optional?

In general, yes.


RTS CTS is required with PC bios programs. Even though it didnt work and
they had to use XON/XOFF. Just loop CTS back to RTS at PC end, set modem to
XON/XOFF.



Modem wont like it at first, but you can tell it to ignore DTR.

Windows dialling programs might not like it if you dont connect DCD. (loop
DTR back to DCD at PC end )


Linux can be set for three wire - stty commands would be like -crtscts
+ixon +ixoff -modem

 

[C3]

thanks for your help, guys.

C3

 

[David Milne]

C3 wrote:

I want to quickly build a serial cable to connect a modem to my serial port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?

C3

There are a number of ways to connect devices together using rs232.
Try this website.

http://www.airborn.com.au/rs232.html

--

Regards
David

=================================
Reply to

dmmilne at ozemail dot com dot au

 

[Roger Lascelles]

Connect all 9 pins on your PC serial connector.

If you do this, it will work, and you can get on with your life. If you get
smart and leave out a wire, you will have the luxury or working out a
spacial initialization string for your modem, and even then it may not work,
or your fax program may not work etc. Trust me, I work with modems, serial
comms & PCs and you need the wires.

Roger


"C3" <user@host> wrote in message
news:3fd66b05$0$1020$afc38c87@news.optusnet.com.au...

I want to quickly build a serial cable to connect a modem to my serial
port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?


C3

 

[Alan Rutlidge]

"Roger Lascelles" <r.o.g.e.r.l.a.s.@optusnet.com.au.removedots> wrote in
message news:3fd6e6a9$0$1025$afc38c87@news.optusnet.com.au...

Connect all 9 pins on your PC serial connector.

If you do this, it will work, and you can get on with your life. If you
get
smart and leave out a wire, you will have the luxury or working out a
spacial initialization string for your modem, and even then it may not
work,
or your fax program may not work etc. Trust me, I work with modems,
serial
comms & PCs and you need the wires.

Roger

I tend to agree with Roger.
Hardware flow control is more efficient than software flow control. Sure,
it is possible to use less wires, but making up a cable with less than 9
wires may work okay with one device and cause merry hell with another.

Is there any real reason for wanting to use a minimum of conductors other
than having less to connect / solder or whatever? Any problems with
debugging / working out which wires are essential and which are not can
rapidly consume more time than connecting all the conductors.

Cheers,
Alan

"C3" <user@host> wrote in message
news:3fd66b05$0$1020$afc38c87@news.optusnet.com.au...
I want to quickly build a serial cable to connect a modem to my serial
port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?


C3

 

[C3]

Well, I may as well reveal what I'm doing. I wanted to hook up my old
Telstra CyberSurfr cable modem up to my computer using the serial port, just
to see whether you could talk to the modem through a shell of some sort. I
tried hooking it up using three serial lines (GND,RX,TX) but even at a
variety of bit rates, it would not talk back.


C3

Is there any real reason for wanting to use a minimum of conductors other
than having less to connect / solder or whatever? Any problems with
debugging / working out which wires are essential and which are not can
rapidly consume more time than connecting all the conductors.

 

[Ken Taylor]

"C3" <user@host> wrote in message
news:3fd729f8$0$1020$afc38c87@news.optusnet.com.au...

Well, I may as well reveal what I'm doing. I wanted to hook up my old
Telstra CyberSurfr cable modem up to my computer using the serial port,
just
to see whether you could talk to the modem through a shell of some sort. I
tried hooking it up using three serial lines (GND,RX,TX) but even at a
variety of bit rates, it would not talk back.


C3

Is there any real reason for wanting to use a minimum of conductors
other
than having less to connect / solder or whatever? Any problems with
debugging / working out which wires are essential and which are not can
rapidly consume more time than connecting all the conductors.

Try using a null modem cable then. Check the DSE catalog or the web if you

need the wiring pinout.

Ken

 

[Rod Speed]

"Alan Rutlidge" <rutlidge*nO-sPaM*@mail.iinet.net.au> wrote in message news:3fd718f5$0$1724$5a62ac22@freenews.iinet.net.au...

"Roger Lascelles" <r.o.g.e.r.l.a.s.@optusnet.com.au.removedots> wrote in
message news:3fd6e6a9$0$1025$afc38c87@news.optusnet.com.au...
Connect all 9 pins on your PC serial connector.

If you do this, it will work, and you can get on with your life. If you
get
smart and leave out a wire, you will have the luxury or working out a
spacial initialization string for your modem, and even then it may not
work,
or your fax program may not work etc. Trust me, I work with modems,
serial
comms & PCs and you need the wires.

Roger


I tend to agree with Roger.
Hardware flow control is more efficient than software flow control. Sure,
it is possible to use less wires, but making up a cable with less than 9
wires may work okay with one device and cause merry hell with another.

Is there any real reason for wanting to use a minimum of conductors
other than having less to connect / solder or whatever?

Yes, you can use those RJ11/RS232 adapters and use standard
phone extension cords for a very quick and convenient connection.

Any problems with debugging / working out which wires
are essential and which are not can rapidly consume
more time than connecting all the conductors.

Sure.

"C3" <user@host> wrote in message
news:3fd66b05$0$1020$afc38c87@news.optusnet.com.au...
I want to quickly build a serial cable to connect a modem to my serial
port.
What are the absolute minimum pin connections I need to make?

Obviously, I'll need RX<-->RX, and TX<-->TX. Are all the other signals
optional?


C3

 

[C3]

I tried swapping the RX and TX wires, but I still couldn't get the modem to
talk.

C3

Try using a null modem cable then. Check the DSE catalog or the web if you
need the wiring pinout.

 

[Franc Zabkar]

On Thu, 11 Dec 2003 11:45:09 +1100, "C3" <user@host> put finger to
keyboard and composed:

I tried swapping the RX and TX wires, but I still couldn't get the modem to
talk.

C3

Try using a null modem cable then. Check the DSE catalog or the web if you
need the wiring pinout.

Modems use "straight-through" connections.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Leon.]

"C3" <user@host> wrote in message
news:3fd729f8$0$1020$afc38c87@news.optusnet.com.au...

Well, I may as well reveal what I'm doing. I wanted to hook up my old
Telstra CyberSurfr cable modem up to my computer using the serial port,
just
to see whether you could talk to the modem through a shell of some sort. I
tried hooking it up using three serial lines (GND,RX,TX) but even at a
variety of bit rates, it would not talk back.

See page 36 (section 1 -26 ) http://membres.lycos.fr/kabelsite/files/013.pdf

for the cross connection between a 25 pin connector on a PC and the 9 pin on
the cybersurfer.


This is not a data modem, this serial port is for diagnostics and
configuration.


You might get by without RTS CTS- but you could just wire it correctly.

If you do try 3 wire ..

On the PC tell your terminal software to use no flow control.
On the cybersurfr, you might need to short RTS to CTS at the cybersurfer.

That should be enough.

But you might need to short DTR, DSR and DCD at the cybersurfer.

AS for speed, the cybersurfr might autodetect, or it might be fixed to some
speed and bit pattern.

If it autodetects and you dont have rts cts flow control, choose a nice slow
speed, or else it will outpace your terminal program and cause garbled text.