HU192925B - Circuit arrangement for realizing circuit sensing state of loop, in particular to processor controlled digital sub-exchanges - Google Patents

Abstract

A line loop detector suitable for analogue and digital subexchanges is provided with two outputs: -for indicating a closed loop -for indicating earthing of branch "a". The output points can be scanned by a processor with the aid of an addressed multiplexer circuit 5. A SLIC circuit 1 monitors the loop, while a voltage comparator 3 is used for monitoring the earthing of branch "a" connected to branch "b". <IMAGE>

Description

In telephone technology, electronic SLIC (subscriber loop interface circuit) circuits are widespread, but most types of circuits do not allow the use of telephone sets with a grounding button. They do not include a separate branch monitoring circuit, but they have the capability to enter stand-by mode when any branch of the telephone line is grounded.

The SLIC circuits have a loop status indicator HSO output which indicates whether the loop is in high impedance (loop open) or low impedance (loop closed).

This output is disabled in standby mode, which is the same as high impedance termination. In PBX networks, it is essential to use a grounding button, which links the branch of the telephone line to ground potential, thereby initiating eg. city line call, handover.

It is an object of the present invention to provide, in addition to the loop status indicator output, a new sensor output that detects a branch ground and at the same time does not display a level corresponding to the standby state in the loop status indicator.

A solution for detecting the grounding of a branch by observing the difference in currents of a, b branches is known. This can be a two-coil relay or an electronic circuit. This solution is not applicable to the SLIC circuits described above because of the off-state caused by the branch ground.

There is also a solution where that branch's potential is monitored. The disadvantage of this solution is that the monitoring circuit cannot distinguish whether the branch has been grounded due to an interruption of a loop or the pressing of a grounding button. This monitor output cannot be used to clear the off state signal from the loop status output.

The processor controlled digital PBX extension circuit sensor circuit shall meet the following requirements.

There are two types of information to provide for softwares evaluation.

- The loop is low impedance or high impedance.

(This information cannot be changed by that branch ground.)

- That branch is grounded or not, this condition can only occur in the low impedance state of the loop.

- this information must be provided for two separate outputs.

The implemented hardware circuit should fit both the mechanical scope and the electrical parameters (voltage demand, power demand, disturbance) to the overall circuit system design.

It should be feasible with a minimum number of parts.

The following circuit meets these requirements.

The lines a and b of the telephone line are powered by an electronic SLIC 1 circuit through controlled current generators, one of which is a - Ui. voltage, another is related to the earth. The currents of the branches a and b are detected by the TSI and RSI inputs of the SLIC 1 circuit which control the current generators by switching on the current generators when the loops a and b and the circuit of the telephone are otherwise closed. In the event that either branch a or b leads to ground, it will be detected by one of the TSI or RSI inputs and will turn off both current generators, causing the SLIC 1 circuit to stand-by. The SLIC 1 circuit has a loop status monitor HSO output. This output gives logic 1 if the loop is closed and C is given if the loop is broken or slave led the SLIC 1 circuit is set to stand-by with information about the SLIC 1 circuit also in TSI and RSI wins.

Another function of the SLIC 1 circuit is to provide audio frequency transmission and 2/4 wire conversion.

The audio signal is received at input Rx and through the current generators is in opposite phase to branches a and b. The audio signal from branches a and b is output to the Tx output.

Also included in the circuit according to the invention is a comparator 3 whose non-inverting input is connected to a branch b via a high impedance 2 while its inverting input is connected to a -Uf reference voltage equal to or less than the most negative of the earth potentials value. The output of the comparator 3 is connected to a gate circuit 4 and to an input of the multiplexer circuit 5. The other input of the cap current 4 is connected to the HSO output of the SLIC circuit 1 and its output is connected to the B input of the multiplex circuit 5.

The above embodiment layout works as follows:

When the loop is closed, which corresponds to the raised handset, the HSO output of the SLIC 1 is tilted logically 1 through the gate circuit 4, which in this case is an OR gate, to the input B of the multiplexer circuit 5, which is addressed through the C pin. , its status goes to data line D. The multiplexer circuit 5 has n numbers of inputs A and B so that it can read n number of subscriber circuits, as detailed in the previous 25.

By pressing the earth button Kf, the SLIC 1 circuit is put into stand-by mode as described above. Since the branches a and b 5 are then connected via the raised handset and the current in the loop is minimal, the potential of branch b will be nearly equal to that of its branch, which has a potential greater than -Ur. The voltage of branch b is detected by comparator 3 through high impedance 2, which at rest has a non-inverting input negative than the inverting input, and therefore has an output of logic 0.

If this voltage of branch b becomes more positive than -Uf, comparator 3 will overturn and logic 1 will be output. If the branch a is grounded with the earth button Kf in the handset's suspended state, the effect of the ground will not appear on branch b due to the loop interrupted state and thus the potential of branch b will be more negative than the reference voltage -Uf and the comparator output will remain 0.

The logic level at the HSO output of the SLIC 1 circuit and at the output of the comparator 3 clearly describes the state of the loop. The logic evaluation is facilitated by the gate circuit 4 (in this case, an OR gate), which causes the logic level 0 on the HSO output to be ineffective by grounding, so that the gate circuit output 4 remains logical 1 when Kf earth button is pressed.

According to the open or closed loop or Kf ground button on the HSO output, the multiplexer circuit 5 or A, respectively. Input B can be displayed at the logical password level as shown in the following table:

loop kf HSO THE B torn Who 0 0 0 torn on 0 0 0 closed Who 1 0 1 closed on 0 1 1

It can be seen from the table that logic 1 at input B represents the hooked-in handset and logic 1 at input A indicates the use of the earthing button Kf.

The telephone cable may be grounded permanently due to a short to ground or a failure of the earthing button Kf. Such errors can be diagnosed such that if input A is in a steady state logic 1, or change in input A has not been preceded by a change in input B indicating input, the ground fault of the telephone line can now be detected by softwares. The ground b short of b, which usually means the other branch, can be detected by the softwares test even when the handset is down.

Claims (2)

A loop state sensor circuit for processor-controlled electronic telephone PBXs, in particular digital telephone PBXs, comprising a SLIC circuit, a multiplexer circuit, characterized in that an auxiliary line interface SLIC circuit (1) is connected to the telephone lines a and b, its branch is connected via a high impedance (2) to one of the inputs of the voltage comparator · (3), the other input of the comparator (3) is connected to a reference voltage -Uf and the output of the comparator (3) is connected to one of the inputs (A) and the output (HSO) of the SLIC circuit (1) is connected directly or indirectly to another input (B) of the multiplexer circuit (5). The loop status detector circuit according to claim 1, characterized in that the output (HSO) of the SLIC circuit (1) is connected to one of the inputs of a gate circuit (4) connected to the other input (B) of the multiplexer circuit (5) and the output of the comparator circuit (3) is connected to one of the inputs of the gate circuit (4) and to one of the inputs (A) of the multiplexer circuit (5).