Why do I have to set the MSN number on a ISDN modem

Load MSN in the ISDN Module.

By default, the ISDN Module will answer all incoming calls on the line. This is only acceptable if exactly one module is connected on the line. If several ISDN Module (or also phone devices) are connected on the same line, it is necessary to load the MSN on each device to be able to select the responding device for each call. In each device, the MSN is considered as valid if the defined digits match the last digits of the called numbers. Therefore, only the 2 last digits are usually required.

With the Modem library, use the corresponding Fbox to load the MSN in the ISDN Module.

If the ISDN Module is not initialized by the library (it's always the case when S-Bus PGU with Modem is configured), the MSN must be loaded in the Module manually (for instance with Hyperterminal) using the following commands. The MSN is automatically stored in non volatile memory. It will remain valid, even after power down, reset and AT&F command. It is cleared however with the AT&F1 command.