Telephone PBX with preselected evaluation - has multiple utilisation of extension control unit for loop stage cyclic testing

摘要

The preselection evaluation deals with the first dialled digit in order to distinguish between directional and special digits for dialling tow-digit numbers of internal extensions. The first dialled digit is received in a binary store in a connecting circuit connected to the calling extension, evaluated there by a preselection evaluation device, and when a directional or special digit is recognised, it is transmitted to the extension control device; when a complete dialling is recognised, the stored digit is converted and then re-applied to the binary store as a new binary signal; the second dialled digit is added to it, and the whole number passed to the extension control device.