| 摘要 |
PURPOSE:To omit a relay within a subscriber circuit and to simplify a busy tone transmission system by providing a digital busy tone generating circuit within the subscriber circuit and connecting the output of said busy tone generating circuit to the input of a decoder while a switchboard is kept under a link block state. CONSTITUTION:A busy tone transmitter BT is provided to a subscriber circuit SUB of a busy tone transmission system. Thus a digital busy tones are produced. While the input given from a highway HW and the output of the transmitter BT are applied to AND gates G1 and G2 respectively. A control circuit CTL controls both gates G1 and G2 as well as an amplifier AMP1 containing a gate. If a link block state is secured when a subscriber picks up the receiver of a telephone TEL, a CPU transmits a non-permission signal for use of a call TS signal producing circuit TS to the circuit CTL. This signal is sent to gates G1 and G2 from the circuit CTL. Thus both gates are opened, and the output of the transmitter BT is supplied to a decoder within a CODEC. |
