Abstract: A time division multiplex private automatic branch exchange includes a common interchange bus, and as many sampling circuits and associated recirculating shift registers as there are telephones. Two telephones are connected to each other through the bus when time-slot-determining outputs of the respective two shift registers actuate transmission gates in the respective sampling circuits. Other pairs of telephones may be connected to each other during other time slots. Additional sampling circuits and shift registers are provided to connect dial tones, ring tones, etc., over the bus to appropriate telephones in the same time division sampling fashion. All sampling connections are made under control of a computer by loading information into time slot stages of the shift registers.