JPH06289964A - Interface circuit - Google Patents

Abstract

PURPOSE:To prevent errorneous judgement and to improve reliability by immediately reporting to the effect that a fuse is cut off. CONSTITUTION:When the fuse F1 is not cut off, a switch S1 is turned off. Thus, device power source VA is supplied to power source for terminating resistance use VB through D1, S1 and F1. Resistances R3, R4, R5 and R6 are set so that the voltage on a negative input terminal in a comparator 3 becomes higher than the prescribed voltage of a positive input terminal. When the fuse F1 is cut off, the voltage on the negative terminal of the comparator 3 becomes a value close to '0'. Thus, the prescribed voltage of the positive input terminal becomes higher than the voltage of the negative input terminal, and the system of the comparator 3 becomes an 'H'-level. Thus, the output terminal of a buffer 4 inverting polarity is grounded and current flows through a light-emitting element 5 and is lighted. Thus, the cut off of the fuse F1 can be informed by the lighting of the light-emitting element 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interface circuit for interconnecting information processing devices and peripheral devices thereof, and more particularly, means for supplying a power supply for a terminating resistor to an interface circuit of another connected device. The present invention relates to an interface circuit including.

[0002]

2. Description of the Related Art FIG. 5 shows a prior art example of an interface circuit having means for supplying a power supply for a terminating resistor to an interface circuit of another device connected thereto. The figure shows 2
The figure shows a state in which two devices are connected via an interface circuit, and the dotted line in the center is the connection part, the device to the left of which is powered on, and the device to the right of which is not powered on. That is, power is supplied from the left device to the terminating resistors R11 and R12 in the interface circuit of the right device, and the right device detects the voltage to determine that the left device is powered. In the figure, R1 and R2 are termination resistors, D1, D2, D11 and D.
12 is a diode, S1 and S11 are switches, F1 and F11 are fuses, 1 and 11 are drivers, and 2 and 12 are receivers. In the devices connected to each other as shown in this figure, the level of the interface signal line from the device of the other party is detected even if the other device is not powered, and the device of the other party is detected as described above. It may determine whether the power is on. Such a need is
For example, when a communication device or the like is provided with an active device and a standby device, it can be understood by assuming a case where the active device power source is immediately switched to the standby device.

However, if power is not supplied to the other device and power is not supplied to the terminating resistor from another device, for example, the voltage at the connection point of R11 and R12 in FIG. It becomes unstable, and the level is judged to be '0' or '1' due to noise mixed in. Therefore, if it is judged whether or not the power is turned on by this signal, Even if is not turned on, it may make an erroneous decision that the power is turned on. In order to solve such a problem, in the related art, for example, in the circuit diagram of FIG.
By supplying the power supply voltage to R11 and R12 through the line as shown by the arrow, the voltage at the connection point of R11 and R12 is set to a high potential in this state, and it is confirmed that this point is a high potential. The power-on state is determined by detecting it. In the above description, D1 and D11 are diodes for preventing current from flowing back to the respective power supply units due to the power supply voltage supplied from another device when the power supply to the own device is not turned on. Further, F1 and F11 are fuses for preventing an excessive current from flowing when the power supply is mistakenly short-circuited to the ground or the like. Further, S1 and S11 are switches for turning on and off the power supply for the terminating resistor.

[0004]

However, in the prior art shown in FIG. 5, when the fuse F1 is blown out due to an excessive current, power is not supplied to the terminating resistor of another device. The potential state of the signal on the interface is not maintained correctly, and as a result, malfunction may occur, that is, the state in which the potential of the interface circuit is not detected is because the power of the other device is not turned on. , Or due to a blown fuse cannot be identified. This is because it is not possible to directly know from the outside that the fuse F1 is blown,
Therefore, there is a problem that even if the fuse is blown and malfunction occurs, the cause cannot be immediately known.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a highly reliable interface circuit by immediately reporting when the fuse is blown. I am trying.

[0006]

[Means for Solving the Problems] To achieve the above object,
According to the present invention, in an interface circuit that supplies a power supply for terminating resistance of an interface to the outside via a fuse, a means for detecting that the fuse is in a blown state, and a means for detecting that the fuse is in a blown state,
That the means for notifying the fact is provided, the means for detecting that the fuse is in the blown state is configured to compare the voltage corresponding to the power supply voltage for the terminating resistor to the supply destination with a predetermined voltage, and the fuse blown. The means for notifying the state is configured to include a light-emitting element, the means for notifying the fuse blown state is configured to include a warning sound, the state for supplying the power supply for the terminating resistor and the state for not supplying the power supply. It is characterized in that the fuse blowout detecting means or the informing means is operable only when the supply state is selected.

[0007]

Since the means for detecting that the fuse is blown and the means for notifying the fact when the fuse is blown are provided, the operator can Since it can be known immediately, misjudgment can be prevented.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the interface circuit according to the present invention. Although only the left-hand side device portion shown in FIG. 5 is shown here, the right-hand side may be the same as that shown in this drawing or a conventional one. In the figure, R1 to R8 are resistors, 3 is a comparator using a differential amplifier, 4 is a buffer, and 5 is a light emitting element. According to this configuration, when the fuse F1 is not blown, the switch S
By closing 1, the power supply V _A of the device is D1, S1, F
Power is supplied to the terminating resistor power source V _B via 1 (V _B is supplied to the terminating resistor in another device, for example, R11 and R12 in FIG. 5). R3, R4, R5, and R6 are such that the voltage at the-input terminal (voltage corresponding to the power supply voltage for the termination resistor) of the comparator 3 when F1 is not disconnected is higher than the predetermined voltage at the + input terminal. That is, it is set to satisfy the following equation. {R ₃ / (R ₃ + R ₄ )} · _VA <{R ₅ / (R ₅ + R ₆
)}. ( _VA -Vd) Here, Vd is a voltage drop in D1, S1, and F1.

When the voltage at the-input terminal is higher than the voltage at the + input terminal of the comparator 3, the output of the comparator 3 has a low potential'L '.
Since the output of the buffer 4 of the inverter type for inverting the polarity becomes the “H” level, the light emitting element 5 does not light. On the other hand, when the fuse F1 is blown, the voltage at the-input terminal of the comparator 3 becomes a value close to 0, and the predetermined voltage at the + input terminal becomes higher than the voltage at the-input terminal. Since the output of the container 3 is at the “H” level, the output end of the buffer 4 is grounded, a current flows through the light emitting element 5, and the light emitting element 5 is turned on. Therefore, it is possible to know that the fuse F1 is blown by the lighting of the light emitting element 5.

FIG. 2 is a circuit diagram showing another embodiment of the iterator circuit according to the present invention. The feature of this embodiment is that a buzzer is used as a fuse blown notification means.
That is, in the figure, 6 is a buzzer for issuing a warning sound. Similar to the embodiment shown in FIG. 1, when the fuse F1 is not blown, {R ₃ / (R ₃ + R ₄ )} · _VA <{R ₅ / (R ₅ + R ₆
)}. ( _VA -Vd), the output of the comparator 3 is at the'L 'level and the output of the buffer 4 is at the'H' level, so the buzzer 6 does not ring. On the other hand, when the fuse F1 is blown, the voltage at the negative input terminal of the comparator 3 becomes a value close to 0, so the output of the comparator 3 becomes “H” level and the output of the buffer 4 becomes “L”. 'Because it is a level, buzzer 6 sounds.
Although the buzzer 6 generates a boo sound by a direct current, it may be replaced with a speaker which is an electric circuit for generating an oscillating sound.

As described above, in the embodiment shown in FIGS. 1 and 2, even if the fuse F1 is not blown, the switch S1
Is off, it works exactly as if F1 were disconnected. That is, the lighting of the light emitting element and the ringing of the buzzer can be controlled by turning ON / OFF the switch S1. However, in order to further improve usability, the following may be performed. That is, FIG. 3 and FIG. 4 are circuits showing an embodiment in which a light emitting element or a buzzer can make an alarm only when the switch S1 which is a means for selecting a state in which the power for the terminating resistor is supplied and a state in which it is not supplied is turned on. It is a figure. 3 and 4,
S2 is a switch that is mechanically interlocked with S1 to turn on / off, R9 is a pull-up resistor connected to the power supply line, 7 is an inverter, and 8 is a NAND buffer. As shown in the figure, if S2 is configured to be turned on when S1 is turned on, then the output of the inverter 7 becomes the “H” level, and therefore the output of the NAND buffer 8 corresponds to the output level of the comparator 3. And it becomes'L 'level,' H '
The level of the light emitting element 5 and the buzzer 6 operates in response to this, but when S1 is turned off,
Since S2 is turned off and the output of the inverter 7 is always at the'L 'level, regardless of the output level of the comparator 3,
The output of the AND buffer 8 is always at "H" level,
The light emitting element 5 does not light up and the buzzer 6 does not ring.

In the above embodiment, a light emitting element or a warning sound such as a buzzer is used as a means for notifying a fuse blown state, but the means is not limited to these. Also, as the means for notifying the blown fuse only when the power supply for the terminating resistor is supplied, the method has been described that operates only when the notifying means selects the state in which the power is supplied. It is also possible to configure it to operate only when the power supply is selected.

[0013]

As described above, according to the present invention,
Means for detecting that the fuse is blown,
When the fuse is detected to be in a blown state, a means for notifying the fact is provided, so that the operator can immediately know when the fuse is blown, and the malfunction due to the blown fuse is prevented. It is possible to know immediately.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an interface circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the interface circuit according to the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the interface circuit according to the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the interface circuit according to the present invention.

FIG. 5 is a circuit diagram showing an example of an interface circuit according to a conventional technique.

[Explanation of symbols]

1 ... Driver, 2 ... Receiver, 3 ... Comparator, 4 ... Buffer, 5 ... Light emitting element, 6 ... Buzzer, 7 ... Inverter, 8 ...
NAND buffer, 11 ... driver, 12 ... receiver.

Claims (5)

[Claims] 1. A power supply for a terminating resistor of an interface,
In an interface circuit that supplies the power to the outside via a fuse, the interface circuit is provided with a detection unit that detects that the fuse is in a blown state, and a notification unit that notifies that when the fuse is in a blown state. An interface circuit characterized by that. 2. The detecting means for detecting that the fuse is in a blown state has a function of comparing a voltage corresponding to a power supply voltage for a terminating resistor to a supply destination with a predetermined voltage. The interface circuit according to claim 1. 3. The interface circuit according to claim 1, wherein the informing means for informing the fuse blown state includes a light emitting element. 4. The interface circuit according to claim 1, wherein the informing means for informing the fuse blown state includes a means for emitting a warning sound. 5. A means for selecting a state in which the power supply for the terminating resistor is supplied and a state in which the power supply for the termination resistor is not supplied are provided, and only when the supply state is selected, the fuse blown detection means can be operated or the notification means. 5. The interface circuit according to claim 1, wherein the interface circuit is configured to be operable.