| 摘要 |
PURPOSE:To satisfactorily receive data signal supplied from a circuit regardless of circuit condition by controlling automatically the attenuation of an attenuator according to the circuit situation. CONSTITUTION:If the attenuation value of the attenuator is not proper to the signal received from a circuit 1, the carrier detection signal CD obtained within a MODEM 3 has the value different from the normal one. A timer 13 is set in response to the signal in a protocol whose signal time is previously known. This setting job of the timer 13 is controlled so that the signal CD is turned off before the 2nd pulse of the output of the timer 13 is obtained after the signal CD is turned on in a normal mode. Thus the ON state of the signal CD is repetitively checked for each set cycle of the timer 13. Then a counter 17 is continuously counted up as long as the signal CD is kept under an ON state for calculation of the attenuation value. The attenuation value is increased by an attenuator setting circuit 12 by an amount equal to the count-up value of the counter 17.
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