JPH058903B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention sets a terminal converter to an initial state when the input signal level of a data communication demodulator falls below a specified input level for a certain period of time or more.
This invention relates to a reset circuit for CATV terminal converters.

[Prior Art and Its Disadvantages] In a CATV system, if the data communication signal transmitted from the center to the terminal converter is interrupted, the operation of the terminal converter may become completely impossible. For example, at hotel CATV,
When a check-out command is sent to the terminal converter, operation of the terminal converter is prohibited, but if the data communication signal is cut off at this point, the prohibition of terminal converter operation cannot be canceled by the check-in command, and the TV I can no longer watch Jiyoung.

In addition, if unmanned operation such as station announcements is performed, if the data communication signal is interrupted during broadcasting,
There is a drawback that it becomes impossible to operate the terminal converter, such as turning off the power, after the broadcast ends.

[Object of the Invention] The present invention has been made in view of the above points, and its object is to reduce the signal level input to a terminal converter to below a specified input level for a certain period of time,
An object of the present invention is to provide a reset circuit for a CATV terminal converter, which makes it possible to set the terminal converter to an initial state when normal data cannot be received.

[Summary of the Invention] The reset circuit for a CATV terminal converter of the present invention includes a demodulator for data communication, a carrier sense circuit that determines whether the input signal level to the demodulator is higher than a specified value, and a reset circuit for the demodulator. In a CATV terminal converter equipped with a pulse generation circuit that outputs a reset pulse and a control microcomputer, when the input signal level of the terminal falls below the specified input level for a certain period of time or more, the signal output from the pulse generation circuit is The control microcomputer is reset by the reset pulse.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a CATV terminal converter according to the present invention. In Figure 1, 1 connects the center and terminal converter.
CATV line, 2 is a terminal converter. This terminal converter 2 includes a demodulator 3 for data communication,
A carrier sense circuit 4 determines whether the input signal level to the demodulator 3 is above a specified value, and outputs a reset pulse if the input signal level to the demodulator 3 falls below the specified input level for a certain period of time or more. It is composed of a pulse generation circuit 5 and a control microcomputer 6. 7 is a reset terminal of the control microcomputer 6.

FIG. 2 is a block diagram showing the configuration of the pulse generating circuit 5. As shown in FIG. In the figure, 8 is the first monostable multivibrator, and 9 is the carrier sense circuit 4.
NAND circuit 10 which calculates the AND of the output signal of the first monostable multivibrator 8 and the output signal of the first monostable multivibrator 8;
is the second monostable multivibrator.

Next, the operation of the above CATV terminal converter will be explained. FIG. 3 shows its operating waveform.

A data communication signal with a carrier frequency of 70.08MHz, which is frequency-modulated with data, is constantly transmitted from the center to the CATV transmission line. A data communication demodulator 3 demodulates the signal and transmits the data to a control microcomputer 6. The control microcomputer 6 controls the terminal converter 2 based on the above data.

This signal is 5V if the input signal level a is above the specified input level, and is 5V if it is below the specified input level.
Becomes OV.

When the input signal level of the demodulator 3 falls below the specified input level in the part B or part C as shown in a, the carrier sense circuit 4 determines this, and
A signal shown in is output to the pulse generation circuit 5. In the pulse generation circuit 5, the monostable multivibrator 8 first detects the falling point of the signal b, and from this point
t Outputs a 5V pulse c for ₁ second. NAND circuit 9
calculates the logical product of the b and c signals, and outputs a 5V pulse only while the b and c signals are both OV, as shown in d.

If the time for the input signal level a to fall below the specified input level a is less than t ₁ second as shown in part B,
Although the output signal d of the NAND circuit 9 does not become 5V,
This is to prevent the control microcomputer 6 from being reset when the input signal level a falls for less than _t1 seconds, which does not interfere with the operation of the terminal converter 2. The monostable multivibrator 10 detects the rising point of the output signal d of the NAND circuit 9, generates a reset pulse e that becomes OV for t ₂ seconds from this point, and transmits it to the reset terminal 7 of the control microcomputer 6 for control. The microcomputer 6 is reset. _t2 is the time required to reset the control microcomputer 6. When the control microcomputer 6 is reset, the terminal converter 2 is set to the initial state and the power switch is turned off, but after that the various switches of the terminal converter 2 can be operated.

[Effects of the Invention] As described above, according to the present invention, when the input signal level of the data communication demodulator in the CATV terminal converter falls below the specified input level,
By resetting the control microcomputer, the terminal converter is set to its initial state,
It is possible to enable operation of a terminal converter. Furthermore, if necessary, all terminal converters can be reset at once by forcibly cutting off the data communication signal transmitted from the center.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a terminal converter according to an embodiment of the present invention, Fig. 2 is a block diagram showing a pulse generation circuit used in the converter, and Fig. 3 shows the operating waveforms of each part of the same embodiment. be. 1... CATV transmission line, 2... Terminal converter, 3... Data communication demodulator, 4... Carrier sense circuit, 5... Pulse generation circuit, 6... Control microcomputer, 7... Reset terminal.

Claims (1)

[Claims] 1 A demodulator for data communication, a carrier sense circuit that determines whether the input signal level to the demodulator is above a specified value, and a carrier sense circuit that determines whether the input signal level to the demodulator falls below the specified input level for a certain period of time or more. In this case, the CATV terminal converter is equipped with a pulse generation circuit that outputs a reset pulse and a control microcomputer, and the control microcomputer is reset by the reset pulse output from the pulse generation circuit. Reset circuit for CATV terminal converter.