Digital switching system with shared analog line

The present invention relates to using analog devices with digital switching systems (DSS), for example Digital private branch exchanges (PBXs) and digital Key System Units (KSUs), which provide connections to digital devices. An auxiliary connection mechanism for allowing a Digital Switching System (DSS) to share an analog line with an analog device (via an auxiliary device port) is disclosed. The auxiliary connection mechanism includes a pair of relays for releasably connecting the auxiliary device port and the DSS to the analog line. When the analog line is idle, both the analog device and the DSS are connected to the line in order to receive incoming calls on the analog line. However, once one of the devices (either the analog device or the DSS) uses the line, the other device should not access the line. A busy line detect circuit is included to detect whether a device is using the line.