JPS631486Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a modem that can switch between 4-wire and 2-wire operation among modems (hereinafter referred to as modems) that perform data communication using lines. The present invention relates to a line loopback test circuit in the state.

A conventional modem line loop test circuit capable of switching between four-wire and two-wire operation is shown in FIG. In FIG. 1, 1 is a modem, 2 is a line, 3 is a transmitting section, 4 is a receiving section, 5 is a line section consisting of a transformer, and 6 is a receiving section for four-wire operation consisting of a transformer. The line parts 7, 8, 9 have strap terminals, 10, which can be switched according to 4-wire and 2-wire operation.
11 is a switch circuit that switches to the line loopback test;
12, 13 and 14, 15 are their contacts, and 16 is a terminating resistor of the receiving line section 6. For four-wire operation, strap terminals 7, 8, and 9 connect terminals 7 and 8.
is strapped. In two-wire operation, strap terminals 7, 8, and 9 are strapped to terminals 7 and 9. Further, the output impedance terminating resistor 16 of the transmitter 3 is equal to the characteristic impedance of the line, and the input impedance of the receiver 4 is sufficiently higher than this. In this circuit, in 4-wire operation, 4
Like a wire-only modem, the transmitter and receiver are completely separated and operate independently.

Two-wire operation is as follows. In the transmission mode of normal operation, a transmission signal is sent from the transmission section 3 to the line 2 through the line section 5. At this time, the transmitted signal also loops around to the receiver 4, but in the two-wire operation transmission mode, the received signal is inhibited, so there is no problem. Further, impedance matching with the line is achieved by the output impedance of the transmitter 3. Since the input impedance of the receiving section 4 is sufficiently high compared to the characteristic impedance of the line,
Does not affect impedance matching. In the receiving mode of normal operation, the received signal enters the receiving section 4 from the line 2 through the line section 5. At this time, impedance matching with the line is achieved by the output impedance of the transmitter 3, as in the transmission mode. As in the transmission mode, the input impedance of the receiver 4 does not affect impedance matching. In the line wrap test, switch circuits 10 and 11 switch to contacts 13 and 15. In the line loopback test for two-wire operation, loopback is not performed to the line side, but only loopback is performed inside the modem. The signal is sent out from the transmitter 3 as in the case of normal operation, and is returned to the receiver 4 via the strap terminals 9 and 7. In this way, the transmitted test signal and received signal are compared, and a line return test is performed. In this case, since the transmitting section 3 becomes unterminated, the level reflected back to the receiving section 4 increases by 6 dB. In general, modems have the same maximum transmitting level and maximum receiving level, which has the disadvantage that this may exceed the receiving level range, making it impossible to perform a correct line return test.

In order to solve these drawbacks, the present invention is designed to terminate the transmitting section during a line loopback test using the line terminating circuit of the receiving line section in four-wire operation.

FIG. 2 shows an embodiment of the present invention, in which numerals 1 to 16 are the same as those in FIG. In two-wire operation, strap terminals 7, 8, and 9 are connected to terminals 7 and 9. Further, the output impedance of the transmitting section 3 and the terminating resistor 16 are equal to the characteristic impedance of the line, and the input impedance of the receiving section 4 is sufficiently high compared to this. In this circuit, in the line loop test,
Switch circuits 10 and 11 have contacts 13 and 1
5, and the transmitter 3 and receiver 4 of the modem are disconnected from the line 2. The transmitting section 3 is connected via the line section 5 and switch circuits 10 and 11 to the receiving line section 6 in four-wire operation, and is therefore terminated by a terminating resistor 16. Therefore, in the line loopback test, the level of the signal looped back to the receiver 4 does not rise to exceed the reception level range, so that the line loopback test can always be performed correctly.

FIG. 3 shows another embodiment of the present invention, in which switch circuits 10 and 1 in the embodiment shown in FIG.
1 is moved to the front stage of the line section 5 and the receiving line section 6 in four-wire operation. In the circuit shown in FIG. 3, the transmitting section 3 is also connected to the terminating resistor 16 via the switch circuits 10 and 11 and is terminated.
Therefore, the level of the signal returned to the receiver 4 does not rise and exceed the reception level range during the line return test, so that the line return test can always be performed correctly.

As explained above, according to the present invention, the transmitter can be terminated even during a line return test, so the level returned to the receiver will not rise and exceed the reception level range, and the line will always be returned correctly. I can take the test.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional line loopback test circuit, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a block diagram showing another embodiment of the present invention. 3... Transmission section, 4... Receiving section, 5... Line section,
6... Reception line section in 4-wire operation, 10,1
1...Switch circuit for switching to line loopback test.

Claims (1)

[Claims for Utility Model Registration] 1. Transmitting section 3, receiving section 4, line section 5, receiving line section 6, switch circuits 10 and 11 for switching to line return test, and 4-wire and 2-wire systems. In a modem device that is equipped with a contact circuit section for switching operation and performs data communication using a line, when the contact circuit section is switched to a two-wire operating state and a line loopback test inside the modem device is performed, the switch circuit described above is used. 10 and 11 to the line loopback test state, the transmitting section 3 and receiving section 4 of the modem are separated from the line 2, and the line termination circuit 16 of the receiving line section 6 is connected to the contact circuit section and the switch circuit 1.
0 and 11, and the output end of the transmitter 3 is terminated by the line terminating circuit 16. 2. The output impedance of the transmitting section 3 and the impedance of the line termination circuit 16 of the receiving line section 6 are made equal to the characteristic impedance of the line 2, and the input impedance of the receiving section 4 is made sufficiently compared to the characteristic impedance. 2. A line loopback test circuit for the modem device according to item 1, which has a higher height.