1. Technical Field
The present invention relates to a facsimile apparatus which is connectable with a plurality of telephones (handsets) and which allows extension-line-communication between the telephones.
1. Background Art
For example, a conventional facsimile machine of the above-mentioned type is connected with a built-in handset and a second handset and allows extension-line-communication between these handsets. It would be convenient if an in-house handset user would be informed of the fact that a call comes from outside (e.g., a communication terminal) during the in-house or extension line communication. Generally, the conventional facsimile machine activates a buzzer, which is incorporated therein, to give notice of such a calling.
However, since the conventional facsimile machine only makes a buzzer sound, the in-house handset user cannot know whether it is a call from a person or a facsimile machine. Accordingly, the user on the called side should interrupt his/her conversation when he/she hears the buzzer, and then determine whether a voice or a facsimile signal is transmitted from outside. If a voice is heard, the user on the called side will talk with the calling person without any inconvenience. However, if it is a facsimile signal, the user should switch the connection of the line or trunk from the telephone to the facsimile machine to receive the facsimile signal. This is inconvenient and troublesome.
Another type of conventional facsimile apparatus has a facsimile communication control module connected with a communication line. (A branch telephone of the facsimile apparatus is also connected with the line.) In this arrangement, in order to detect on-hooking and off-hooking of the branch, telephone, the conventional facsimile apparatus generally includes a hook detector circuit which determines the hooking state of the branch telephone by comparing the voltage of the line with a reference voltage. When the branch telephone is off hooked, the voltage of the line generally drops, for example from 48 V to about 10 V. Taking advantage of this, an appropriate value between 10 V and 48 V is chosen as the reference voltage and it is compared with the voltage of the line. If the former is lower than the latter, the facsimile apparatus judges that the branch telephone is on-hooked. Otherwise, it is judged that the branch telephone is in an off-hook state. In short, the conventional facsimile apparatus employs an analog hook-state detecting circuit to determine the on/off hooking of the branch telephone.
If a second handset is further attached to the facsimile apparatus via a modular jack, it is necessary to detect dial pulses from the branch telephone and the second handset before a call from outside is transferred to the branch telephone or the second handset or when a user of one handset wants to talk to another user of the other handset. In this case, the conventional facsimile apparatus analogously processes the voltage of the line during generation (or transmission) of the dial pulses to detect the number of the dial pulses. Specifically, the number of the dial pulses is determined based on output from a photocoupler which detects an off-hooking of the telephone (or handset). The dial pulse originally has a rectangular or square waveform as illustrated in FIG. 10 of the accompanying drawings, but the waveform may have crackings as depicted in FIG. 11 for various reasons. If the dial pulse has such a waveform, it is not possible to correctly determine the number of the dial pulses.
This type of facsimile apparatus is desired to receive a facsimile signal from outside without making any sound (ringing or bell sound) at a built-in handset when a ringing signal is transmitted from a line switching device, for example, when the facsimile apparatus is in a dial-in mode (a mode for a direct inward dialing) or a telephone/facsimile mode. Conventionally, in order to perform such a no-ringing reception, a relay switch between the communication line and the built-in handset is turned off to disconnect the built-in handset from the communication line.
For this end, however, the conventional facsimile apparatus should include a relay switch to connect and disconnect the built-in handset with/from the communication line so that an additional cost for such a switch is required and a switching control for the switching operation is also necessary.
In addition, since the conventional facsimile apparatus turns off the relay switch to disconnect the built-in handset from the communication line, it is impossible to use various functions and elements incorporated in the built-in handset such as a speech network during the disconnected state.