SLIP Modem dial-up sequence

I'm trying to connect a Windows PC to an embedded system via an RS232 link 
implementing SLIP. Ultimately I'll have a web server running on the embedded 
system.
It seems that the only way to do this at the Windows end is to configure a 
dial-up with SLIP selected and pointing to an imaginary modem on COM1/2. At 
the embedded end I need to mimic the behaviour of a modem until the 
connection is set-up. I thought that all this would entail would be to send 
'OK<LF><CR>' after receipt of each AT command. However this isn't the case. 
I can get the Windows dial-up as far as Dialling but then it times out, 
presumably waiting for some response.

Does anyone know what the expected sequence of commands and responses is in 
this case please?

TIA,

Rog 

"Roger" <rogerwilson@hotmail.com> wrote in message
news:gBbFd.174$QV5.146@newsfe6-win.ntli.net...
> I'm trying to connect a Windows PC to an embedded system via an RS232 link
> implementing SLIP. Ultimately I'll have a web server running on the
embedded
> system.
> It seems that the only way to do this at the Windows end is to configure a
> dial-up with SLIP selected and pointing to an imaginary modem on COM1/2.
At
> the embedded end I need to mimic the behaviour of a modem until the
> connection is set-up. I thought that all this would entail would be to
send
> 'OK<LF><CR>' after receipt of each AT command. However this isn't the
case.
> I can get the Windows dial-up as far as Dialling but then it times out,
> presumably waiting for some response.

Well, the "modem" should at least return "CONNECT<cr>" when windows sends
"ADTxxxx". All other AT commands from windows can be responded to by
"OK<cr>" Try to dig up a Hayes command set description.

Meindert

"Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> wrote in message

> Well, the "modem" should at least return "CONNECT<cr>" when windows
sends
> "ADTxxxx". All other AT commands from windows can be responded to by
> "OK<cr>" Try to dig up a Hayes command set description.

The OP should bring up the CD line as well to indicate a connect..

"Anthony Fremont" <spam@anywhere.com> wrote in message
news:IPdFd.3783$%P4.2887@fe2.texas.rr.com...
> The OP should bring up the CD line as well to indicate a connect..

I think tying the DTR,DSR and CD together on the computers' side will do the
job.
Does windows really need the CD?

Meindert

Roger wrote:
> I'm trying to connect a Windows PC to an embedded system via an RS232 link 
> implementing SLIP. Ultimately I'll have a web server running on the embedded 
> system.
> It seems that the only way to do this at the Windows end is to configure a 
> dial-up with SLIP selected and pointing to an imaginary modem on COM1/2. At 
> the embedded end I need to mimic the behaviour of a modem until the 
> connection is set-up. I thought that all this would entail would be to send 
> 'OK<LF><CR>' after receipt of each AT command. However this isn't the case. 
> I can get the Windows dial-up as far as Dialling but then it times out, 
> presumably waiting for some response.
> 
> Does anyone know what the expected sequence of commands and responses is in 
> this case please?

In Windows Dial-up networking select "Direct connection between two 
computers (COM1)". Then select baudrate, protocols, etc. When you dial 
out using that connection Windows will send out the string CLIENT, the 
embedded system would then reply with the string CLIENTSERVER. The 
CLIENT / CLIENTSERVER exchange takes the place of the usual modem stuff.

"Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> wrote
> "Anthony Fremont" <spam@anywhere.com> wrote
> > The OP should bring up the CD line as well to indicate a connect..
>
> I think tying the DTR,DSR and CD together on the computers' side will
do the
> job.
> Does windows really need the CD?

I don't think windows needs it per se, but his application (hyperterm?)
may.  IIRC, I couldn't get hyperterm to send data without it (even with
hardware flow control disabled), but I may well be mistaken on that.  I
tend not to use hyperterm.  ;-)

"Anthony Fremont" <spam@anywhere.com> wrote in message
news:qVvFd.233$Ta2.15@fe2.texas.rr.com...
>
> "Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> wrote
> > Does windows really need the CD?
>
> I don't think windows needs it per se, but his application (hyperterm?)
> may.  IIRC, I couldn't get hyperterm to send data without it (even with
> hardware flow control disabled), but I may well be mistaken on that.  I
> tend not to use hyperterm.  ;-)

Hyperterm definately does not need the CD and if you disable hardware flow
control (affects only DTR/DSR and CTS/RTS) it works fine over 3 wires.

Meindert

Hi Roger,

This is a comment from my 8051 slip code that appears right about where the
problems begin. It might be helpful.

  /* The COM port driver now believes that it has established a DTE
     to DTE link via 2 DCE (modem) devices. If DCD is not asserted
     by the device emulating the local DCE, then the port driver
     decides that the remote modem has hung up. It then shuts down
     the link and tries to hang-up the local DCE.

     The local DTE will assert DTR whenever its ready to send data
     on a newly established link. We can link this to DCD to trick
     the COM port driver into thinking that the local DCE is receiving
     a carrier from the remote DCE, thereby signalling that the remote
     DCE has not hung-up and that all is well. This prevents the
     early SLIP link shut-down.

     On a DB25 connector link pin 20 (DTR) to pin 8 (DCD), or
     for a DB9 connector link pin 4 (DTR) to pin 1 (DCD).           */

Regards,
Murray R. Van luyn.

"Roger" <rogerwilson@hotmail.com> wrote in message
news:gBbFd.174$QV5.146@newsfe6-win.ntli.net...
> I'm trying to connect a Windows PC to an embedded system via an RS232 link
> implementing SLIP. Ultimately I'll have a web server running on the
embedded
> system.
> It seems that the only way to do this at the Windows end is to configure a
> dial-up with SLIP selected and pointing to an imaginary modem on COM1/2.
At
> the embedded end I need to mimic the behaviour of a modem until the
> connection is set-up. I thought that all this would entail would be to
send
> 'OK<LF><CR>' after receipt of each AT command. However this isn't the
case.
> I can get the Windows dial-up as far as Dialling but then it times out,
> presumably waiting for some response.
>
> Does anyone know what the expected sequence of commands and responses is
in
> this case please?
>
> TIA,
>
> Rog
>
>
This is a comment from my 8051 slip code that appears right about where the
problems begin.

  /* The COM port driver now believes that it has established a DTE
     to DTE link via 2 DCE (modem) devices. If DCD is not asserted
     by the device emulating the local DCE, then the port driver
     decides that the remote modem has hung up. It then shuts down
     the link and tries to hang-up the local DCE.

     The local DTE will assert DTR whenever its ready to send data
     on a newly established link. We can link this to DCD to trick
     the COM port driver into thinking that the local DCE is receiving
     a carrier from the remote DCE, thereby signalling that the remote
     DCE has not hung-up and that all is well. This prevents the
     early SLIP link shut-down.

     On a DB25 connector link pin 20 (DTR) to pin 8 (DCD), or
     for a DB9 connector link pin 4 (DTR) to pin 1 (DCD).           */