JPH0323706A - Signal termination circuit - Google Patents

Abstract

PURPOSE:To perform termination in the optimum position without supplying disturbance to a signal bus by automatically switching the terminating position of the signal bus according to the packaging state of a unit by the connection of a control bus. CONSTITUTION:In each of the units 24-44, terminating resistors 2141 connected to a signal line 13, and transistors 22-42 connected between the terminating units 21-41 and the ground inside the unit and control the on and off operations of the connection of the terminating resistors 21-41 to the ground with voltages supplied to their bases are provided. Also, pull-up resistors 23-43 capable of supplying the voltage to turn on the transistors and the control buses 14-16 connected to the bases of the transistors are provided. The control bus is grounded with the unit connected behind the unit, and the control bus 16 of the last panel is opened. Therefore, the terminating position of the signal bus can be switched automatically according to the packaging state of the unit. Thereby, the termination can be realized at the unit located in the farthest position from a signal source.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a signal termination circuit.

[Conventional technology]

Conventionally, the selection of whether or not to use a terminating resistor has been made manually using a mechanical switch inserted in series with the resistor.

In a system having a bus structure in which a plurality of units are connected to one signal line, when terminating a signal, it is necessary to terminate the signal in a unit farthest from the signal source in order to terminate the signal correctly.

[Problem to be solved by the invention]

In the conventional termination switching method described above, if a unit's posture changes, a unit further away appears, or if a unit that is performing trench or termination is pulled out, the signal termination condition changes. However, there was the issue of disturbing the signal.

[Means to solve the problem]

The signal termination circuit of the present invention includes, in each unit of a system in which a plurality of units are sequentially connected to a signal line that requires termination, a termination resistor connected to the signal line, and a terminal between the termination resistor and the unit internal circuit. A transistor connected between the ground and the ground that turns on and off the connection between the terminating resistor and the ground by applying a voltage to the base, and a pull-up resistor that is connected to the base of this transistor and can supply the voltage that turns on the transistor. and a control bus connected to the base of the transistor, the control bus being connected to ground for all subsequent units connected to that unit, and the control bus of the final panel being open. It has a structure.

[Effect]

According to the present invention, the termination position of the signal bus can be automatically switched according to the mounting state of the unit by connecting the control bus.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The figure is a circuit diagram showing an example of the present invention.

In the figure, 11 is a transmitting unit, 12 is a transmitting circuit, 1
3 is a signal bus, 14, 15.16 is a control bus, 21,
31. 41 is a termination resistor connected to the signal line; 22.
32, 42 are the terminating resistors 21, 31 .
41 and the ground air inside the unit, and the terminating resistor 21 , 31 . Transistor that turns on and off the connection between 41 and the earth, 23, 33
．． 43 are respectively connected to the bases of the transistors 22, 32, 42.
Pull-up resistors 24 and 34. 44 is a receiving unit that can supply voltages to turn on the respective pull-up resistors.

The control buses 14, 15, 16 are connected to the bases of the transistors 22, 32, 42, respectively, and the control buses 14-16 are connected to ground for that unit and all subsequent units. The final panel's control bus will be left open.

Next, the operation of the embodiment shown in this figure will be explained.

The output of the transmitting circuit 12 in the transmitting unit 11 is transmitted via a signal bus 13 to each receiving unit }24, 34 . Tori b in 44
Includes 1. And each receiving unit}24, 34.4
Each of the signal buses 13 connected to 4 is connected to a terminating resistor 2.
1,31. 41Th and transistors 22, 32.
42 terminates at the ground. However, although the transistor 22 of the receiving unit 24 is pulled up to +5V by the pull-up resistor 23, since the control bus 14 is dropped to the ground like the other receiving units, the transistor 220 base・The emitter voltage v0 is 0, the transistor 22 is off, the termination resistor 21 is electrically connected to the ground, and the receiving unit 24 is at the termination of the signal bus 13. Do not do this.

Similarly, even if the receiving unit 34 fails, the pull-up resistor 3
Transistor 3 is suspended to 6+5V by 3.
Since the base voltage of the control bus 15 is dropped to the ground by the receiving unit 44, the transistor 32 is also turned off and the receiving unit 34 does not terminate the signal bus 13. Regarding the receiving unit 44, since it is dangerous to drop the control bus 16 to the ground, the base voltage of the transistor 42 is set to the voltage given by the pull-up resistor 43, and the transistor 42 is not turned on. is the termination resistor 41
is terminated by

〔Effect of the invention〕

As explained above, the signal termination circuit of the present invention can automatically switch the termination position of the signal bus according to the mounting state of the υ unit by connecting the control bus, without causing any disturbance to the signal bus. This has the effect of terminating at an optimal position. Since there is no additional human intervention, there is an advantage that mistakes in switch settings can be avoided.

[Brief explanation of the drawing]

The figure is a circuit diagram showing one embodiment of the present invention. 11...●● Transmission unit, 12●●●● Transmission circuit, 1
3...Signal bus, 14-16●...Control bus, 2
1...Termination resistor, 22...●●transistor, 2
3●●●●pull-up resistor, 24...receiving unit, 31...terminal resistor, 32●●●●transistor, 33...pull-up resistor, 34●●●●receiving unit, 41... Termination resistor, 42... Transistor, 4 3 - Pull-up resistor, 4 4 ● - Receiving unit.

Claims (1)

[Claims] In each unit of a system in which multiple units are connected in sequence to a signal line that requires termination, there is a terminating resistor connected to the signal line, and a terminating resistor connected between the terminating resistor and the ground within the unit and the base. a transistor that turns on and off the connection between the terminating resistor and the ground by applying a voltage to the ground; a pull-up resistor that is connected to the base of this transistor and can supply a voltage that turns on the transistor; and a pull-up resistor that is connected to the base of the transistor A signal termination circuit characterized in that the control bus has a configuration in which the control bus is connected to the ground in all units connected after the unit, and the control bus of the final panel is left open. .