Subscriber circuit with AF pushbutton selection for PBX - has special-facility buttons each used twice depending on whether handset is lifted or not

摘要

A pulse generator (IS) is controlled either by special-facility pushbuttons (ST) or from the normal selection keyboard (WT). The special-facility buttons allow various additional facilities like enquiry calls, rerouting, intervention, conferencing etc. to be activated by pressing the appropriate special-facility button - which causes an appropriate sequence of pulses to be generated. The special-facility buttons are arranged so that special facilities can be activated even without lifting the handset. Normally an even number of pulses is generated when a button is pressed. With the handset not lifted whichever is the last pulse is not generated by the subsequent and continuous loop-break so that an odd number of pulses is produced. This odd number activates those special facilities appropriate to an unlifted handset. The special-facility buttons can be used twice e.g. for direct connections to an attendants set in the private branch exchange system or to an extension. The user only has to operate the button for the wanted special detected by a centralised sampling device by counting. Since the pulses generated are temporarily independent of the user's behaviour, the centralised detector can be set to fixed values.