JPH0644221Y2 - Digital Private Branch Exchange - Google Patents

Description

TECHNICAL FIELD The present invention relates to a digital private branch exchange having a memory for digitally encoding and storing signals such as PB signals and tone signals.

2. Description of the Related Art In a digital private branch exchange, PB signals, tone signals, etc. (hereinafter, these signals are collectively referred to as digital signals) are digitally encoded, stored in a memory such as a ROM, and read as necessary. . In this case, in order to reduce the number of digital signal samples stored in the memory, the signal frequency is artificially changed within the permissible error of the regulation of terminal equipment, etc., and the sampling frequency of 8 KHz and the greatest common divisor are set. Has been improved (Japanese Patent Laid-Open No. 59-49093).

Problems to be Solved by the Invention However, in the conventional digital private branch exchange,
Since the transmission level of digital signals such as PB signals is constant, there are the following problems. In other words, the attenuation status of the lines connected to the exchange is different for each line, so if the transmission level of the digital signal is constant, it is difficult to hear the PB sound, etc. on the line with large attenuation, and the level of this is In order to do so, it is complicated to operate a volume controller or the like attached to the telephone.

It is an object of the present invention to provide a digital private branch exchange that automatically adjusts a signal level on the sending side so that a sound volume is always appropriate without performing any complicated operation on the telephone side.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention is a digital private branch exchange equipped with a memory for digitally encoding and storing signals such as PB signals and tone signals. Is stored at a plurality of different levels, and at the time of reading the contents, the signal level is selected based on the detection value of the current detection circuit that detects the current flowing through the station loop.

Action The current flowing through the loop is correlated with the attenuation of the line. That is, if the line attenuation is large, the current flowing through the local loop is small, and conversely if the line attenuation is small,
The current flowing through the office line loop becomes large. Therefore, the signal level of the PB signal and the tone signal is selected by the detection signal of this current, so that the signal of an appropriate level is transmitted according to the attenuation condition of the line, and the volume adjustment operation is not performed on the telephone side at all. You can listen to the PB signal at an appropriate volume without performing it.

Embodiment FIG. 1 shows an embodiment of a digital private branch exchange of the present invention, 1 is a line, 2 is a current detection circuit for detecting a current flowing in a central loop, and 3 is a transmission circuit based on a detection value of the detection circuit 2. A control circuit 4 for generating a control signal for selecting a level to be output is an exchange main body including a digital signal generator, a time switch and the like. As shown in FIG. 2, the digital signal generator in the exchange main body 4 is composed of a ROM 5 as a memory for storing PCM-coded digital signals such as PB signals and tone signals, a counter 6, and a data selector 7. Has been done.

In the ROM 5, PB signals and tone signals are stored at different levels. Figure 3 shows a storage state of the ROM 5, separated into four memory areas in the ROM (O _H ~3FFF _{H,
~7FFF H, ~BFFF H, ~FFFF H} ), stores the PB signal and the tone signal of the four levels of level 0-3 in the respective memory areas. At each level, the PB signal is stored in 16 segments and the tone signal is stored in 8 segments.
The four types of levels 0 to 3 have level 1 as a standard value,
The relationship is Level 3> Level 2> Level 1> Level 0.

Incidentally, the signal frequencies of the PB signal and the tone signal of each level are artificially changed within the allowable range of the regulations of the terminal equipment and the like, as in the conventional case, to reduce the number of samples stored in the ROM. Specifically, since the sampling frequency of the PCM code is 8 KHz, the signal frequency is set so that the greatest common divisor of the frequencies of the PB signal and the tone signal is 20 Hz, and the number of samples to be stored is reduced.

The count value of the counter 6 is input to the address lines A _{0 to} A ₈ of the ROM 5, and the memory contents are periodically read onto the data lines D _{0 to} D ₇ according to the count value. The read memory contents are converted into a serial signal by the data selector 7 and sent to the line 1 through the time switch. Further, a signal for selecting a segment of the PB signal and the tone signal is provided on the address lines A _{9 to} A ₁₂ , a signal for selecting the PB signal and the tone signal is provided on the address line A ₁₃ , and a signal for further selecting the address line A Control signals for selecting the levels of the PB signal and the tone signal are input to ₁₄ and A ₁₅ from circuits outside the figure, respectively. Of these, the level selection control signal is input from the control circuit 3 in FIG.

According to the above configuration, in FIG. 1, when the local loop is formed and the PB signal or the tone signal is transmitted, the current detection circuit 2 detects the current flowing through the local loop 1, and the level is selected through the control circuit 3. Control signal for ROM5 address line
It added to ROM5 through A _14, A _15. Then, ROM5,
If the detected current value is smaller than the standard value, the level 2 or level 3 PB signal or tone signal is selected. If the detected current value is larger than the standard value, the level 0 PB signal or tone signal is selected. Read to. Thus, PB
The volume levels of the signal and tone signal can be automatically changed to appropriate values according to the attenuation status of the line 1.

As described above, according to the present invention, it is possible to send digital signals such as PB signals and tone signals at appropriate levels according to the attenuation condition of the line, so that there is no need to perform complicated volume adjustments on the telephone side. It has the effect of being extremely valuable.

[Brief description of drawings]

FIG. 1 shows a digital private branch exchange showing an embodiment of the present invention, FIG. 2 shows a digital signal generator, and FIG.
It is a figure which shows the memory map in ROM. 1 ... Line, 2 ... Current detection circuit, 5 ... Memory (ROM).

Claims (1)

[Scope of utility model registration request] 1. A digital private branch exchange equipped with a memory for digitally encoding and storing signals such as PB signals and tone signals, in which the signals such as PB signals and tone signals are stored at a plurality of different levels. The digital private branch exchange is characterized in that the signal level is selected based on the detection value of the current detection circuit that detects the current flowing through the local loop when reading the contents.