Werner Johansson
2005-Sep-02 07:56 UTC
[Asterisk-Users] TDM400 w/ FXS S110M pinout on RJ11 connector?
Hi all, I just got my long awaited FXS modules for a TDM400 card, and was a bit puzzled about how my phones and the FXS interface worked together. Here goes: In Sweden (that's where I am located) phones traditionally are connected in daisy chain configuration. This means that a phone in on-hook condition passes the line through back onto the outer pair of the RJ11, back into the wall outlet to the next phone's inner pair. Our phone outlets automatically goes into pass-through mode if no phone is attached (otherwise all outlets has to be connected to phones for it to work). Anyway when I tried just connecting a phone to the FXS module it immediately thought the phone was going off-hook, nothing seemed to help to get it back on-hook. Finally after disconnecting the phone it goes back on-hook. I realised that something was wrong with the pinout when I used a cable with only the inner pair connected and everything just works to work. After some more testing I discover that I'm actually causing a complete _short_ on the battery voltage by looping the inner pair back to the outer pair in the phone! The voltage drops from approx. -48V to 0.0V. To my question: Does anyone know what's actually connected to the outer pair on the TDM400 ports? I guess the only workaround is to only use cables where only the two wires from the inner pair is connected? This might be informative to others trying the same thing as I did, I though it would be a quick way to see that the ports were alive, only to find that they appeared completely broken when I tried.. :| Any educated guesses why the ports are wired as they are? Regards, Werner