S pin in cross cabling DCE - DCE

[Pabxer]

Hi !

We need to connect two DCEs ( multiplexer and NT modem) with X.21 interface.

On mux side there is DB25 connector.Using jumpers it can be set for X.21 and we have pinout scheme in that case.
On modem side we have DB15 port. I suppose standard pinout.

I know we should cross T&R and I&C pins , but what about S (signal timing ) pin. Should we connect it on unsigned pin on other side ?

Thanks

 

[g6udx]

Do you have the pinning for the non-standard DB25 x21 I/F?

 

[Pabxer]

I have following pinout written in documentation for port on multiplexer :


DB25 Pin Assignments
( X.21 Interface to DCE)

3 --> T(A)
16 --> T(B)
2 <-- R(A)
14 <-- R(B)
15 --> C(A)
13 --> C(B)
24 <-- I(A)
23 <-- I(B)
18 <-- S(A)
21 <-- S(B)
7 --- Signal Ground
1 --- Shield

On NT modem side ( we still didn't get it, but we are expecting to get it soon, so we want to prepare in time adequate cable) is standard DB15 port for X.21 interface.

 

[g6udx]

Final question.

DCE usually provides clocking.

In this case which one?

 

[Pabxer]

Well ...

Clocking is supplied to the multiplexer from the NT modem and this NT(ADSL) modem is connected to Telecom from which it gets its clock.