JPH0430210A - Terminal control circuit - Google Patents

Abstract

PURPOSE:To eliminate the setting of the terminal of a bus by means of a manual operation by detaching a terminal circuit based on mounting information received from a downstream and activating the terminal circuit only n an option package in the lowest stream. CONSTITUTION:When an electronic circuit mounting substrate 5 is connected to the bus 6 while electronic circuit mounting substrates 1-4 are connected to the bus 6 and they are operated and a terminal control circuit 12a is operat ed, a mounting information signal 10 in an open state till then comes to L. Thus, the transistor 13 of the terminal control circuit 12a is cut off and a termi nal resistance R is prevented from operating. On the other hand, the mounting information signal of the newly connected electronic circuit mounting substrate 5 comes to the open state but it becomes H because it is pulled up. Thus, the transistor 13 of the terminal control circuit 12b is turned on ad the terminal resistance R operates. Thus, the terminal control circuit automatically operates only in the lowest stream by connection or insertion/extraction and therefore setting by the manual operation becomes unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a structure of a termination control circuit that enables automatic setting of a termination circuit in an electronic device having a bus structure requiring a termination circuit.

[Conventional technology]

Generally known bus termination circuits are available in two ways: mounting the termination circuit separately on the package where the termination circuit is to be mounted, connecting the termination circuit itself from the outside, and installing the termination circuit in a package.

Manual means such as switching the presence/absence of use with a switch etc. were used. On the other hand, JP-A-62-248057
As stated in the publication, for devices that are positioned as upper/lower, there is a method of inputting an address signal and using a voltage comparator to switch and set the termination circuit installed in each device. It was considered.

[Problem to be solved by the invention]

The problem with the above conventional technology is that it involves manual labor for setting the termination circuit, does not take into consideration the diversification of setting methods in modern equipment conditions, and increases the possibility of incorrect settings. was there. Furthermore, in the conventional method, the circuit for switching the termination is complicated, and it is necessary to recognize the upper and lower devices.

The present invention aims to eliminate manual labor and to automatically set a termination circuit without being affected by the device status, and furthermore, the present invention aims to eliminate the need to prepare a termination circuit separately. The purpose is to provide a control circuit.

[Means to solve the problem]

In order to solve the above problem, all packages are equipped with a termination circuit in advance, and each package is connected in turn using a mounting information signal.
RD) and becomes L, and when it becomes open, it becomes high (H) because it is pulled up. The fact that it is open here means that there is no board downstream of it, so it is understood that all it has to do is operate the termination circuit.

Under such conditions, in order to operate the termination circuit only when H is input, the characteristics of the transistor are utilized, a termination resistor is connected, and the 0N10FF is automatically controlled.

[Effect]

When it comes to the most downstream package connected to the bus, the mounting information signal line is open, but since it is powered up at +5V, H is input to the termination control circuit.

As a result, the transistor in the termination control circuit is turned on, and the termination resistor connected thereto operates.

Due to the structure described above, when a package equipped with a termination control circuit is connected and inserted/removed, the termination automatically operates when the package is installed at the lowest level, so it is necessary to set it manually by one person. There is no need to prepare a circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. 1 to 5 are electronic circuit mounting boards consisting of logic elements including termination circuits, 6 is a bus that connects and operates 1 to 5, 7 and 8
is an electronic circuit, 9 and 10.11 are mounting information signals for determining whether there is a device downstream from itself, and 12a and 12b are termination control circuits that are mounted on all electronic circuit mounting boards and operate as necessary. .

With the above configuration, whether or not to operate the termination control circuit is automatically set as follows.

When the electronic circuit mounting boards 1 to 4 are connected to the bus 6 and operating, and the termination control circuit 12a is operating, when the electronic circuit mounting board 5 is connected to the bus 6, the mounting information signal that was in the open state until now is 10 becomes L.

As a result, the transistor 13 of the termination control circuit 12a is cut off, and the termination resistor R no longer operates.

Conversely, the mounting information signal of the newly connected electronic circuit mounting board 5 is in an open state, but it becomes H because it is pulled up, and as a result, the transistor 1 of the termination control circuit 12b
3 is turned on and the terminating resistor R comes into operation. As described above, in the electronic circuit mounting board, the termination control circuit automatically operates only at the most downstream side by connection or insertion/removal.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

By mounting the present invention on an electronic device.

It is possible to eliminate the need to manually set the terminal of the bus. Furthermore, since all the packages are equipped with termination circuits, they can be made the same without providing separate termination boards.

Therefore, it is possible to provide a termination control circuit that can easily switch terminations.

[Brief explanation of drawings]

1 and 2 are simplified diagrams for explaining an embodiment of the present invention, and FIG. 3 is a diagram showing the circuit of FIG. 2. 1.2, 3, 4.5... Electronic circuit mounting board, 6... Bus, 7.8... Electronic circuit, 9, 10
．． 11... Mounting information signal, 12a, 12b... Termination control circuit. Kayuan 7, 2.3.4.5- The anti-bus equipped with Jinkou Road / No. 3 / 2.ノ3-A excluded (toj dawn - 翫周TRI乎-pau, /

Claims (1)

[Claims] 1. Electronic circuit mounting board (
In a system consisting of a package (hereinafter abbreviated as "package"), multiple packages that can be optionally added depending on functions and processing capabilities, a common bus that interconnects these packages, and a termination circuit that terminates both ends of the common bus, When the termination circuit at one end of the common bus is provided on a package that is permanently installed, and the other end is provided on an optional package, the termination circuit at one end of the common bus is provided on the side that is further away from the package that is permanently installed (hereinafter referred to as
Called downstream. The opposite is called upstream. ) is installed in the option package upstream from the most downstream option. A termination control circuit characterized in that only a package activates a termination circuit.