JP2007104353A - Logical setting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a logical setting circuit for detecting an failure in insulation without adding a special diagnostic circuit. <P>SOLUTION: In the logical setting circuit, each voltage at a connection point of two or more logical setting switching means connected to different pull-up resistors or pull-down resistors, is entered in a logical circuit unit. In this case, the pull-up resistors or the pull-down resistors have different resistance values from each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an insulation failure countermeasure for a logic setting circuit that inputs voltages at connection points of a plurality of logic setting switch means connected to different pull-up resistors or pull-down resistors to a logic circuit section.

  As a prior art regarding measures against insulation failure, there is Patent Document 1. FIG. 3 is a functional block diagram showing a configuration example of a conventional logic setting circuit. Reference numeral 1 denotes a logic setting unit, which comprises a plurality of logic setting switch means 11, 12, 13,. One terminal of these switch means is connected in common and connected to the ground potential E. The other terminals of these switch means are connected to an appropriate DC potential + V through pull-up resistors (resistance values R) 21, 22, 23,.

  Signals of connection points V1, V2, V3,... Vn between the switch means and the pull-up resistors are input to the logic circuit unit 3 and compared with a predetermined threshold potential by the setting reading circuit 31 to be digital. Signaled.

  In printed circuit boards on which electronic circuits are mounted, insulation between terminals is caused by corrosion caused by migration due to corrosion caused by the outside air environment (corrosive gas, condensation, etc.) or cracks generated in the flux residue in the soldering process. Defects may occur.

In an electronic device path that requires reliability, it is necessary to take measures against a logic malfunction caused by this insulation failure. As a general countermeasure against corrosion such as migration of electronic equipment,
(A) Use of a substrate material having excellent corrosion resistance and a flux that suppresses the occurrence of migration.
(B) Use a sealed structure to prevent the entry and condensation of corrosive gases.
The method is adopted.

  Patent Document 1 describes a contact input circuit having a pull-up resistor.

Japanese Patent No. 2863775

The conventional logic setting circuit has the following problems.
(1) The above-mentioned general measures require the use of special materials and a highly airtight casing, which causes a significant cost increase of the equipment.

(2) In place of such a general countermeasure, there is also a technique in which a corrosion diagnosis circuit is provided to detect a failure and replace the substrate before being affected by an insulation failure. However, since the conventional logic setting circuit itself does not have a corrosion diagnosis function, it is necessary to add a new expensive diagnosis circuit, which also causes a significant cost increase.

  The present invention has been made to solve the above-described problems, and an object thereof is to realize a logic setting circuit capable of detecting an insulation failure without adding a special diagnostic circuit.

In order to achieve such a subject, the present invention has the following configuration.
(1) In a logic setting circuit for inputting voltages at connection points of a plurality of logic setting switch means connected to separate pull-up resistors or pull-down resistors to a logic circuit unit,
A logic setting circuit, wherein the pull-up resistor or the pull-down resistor has different resistance values.

(2) The logic setting switch means based on a predetermined threshold voltage set in the logic circuit section when an insulation failure occurs between adjacent connection points of the logic setting switch means under the same condition. The logic setting circuit according to (1), wherein the pull-up resistor or the pull-down resistor has a different resistance value so that the logic input value of 1 changes by 1 bit.

(3) The logic setting circuit according to (2), wherein the logic circuit section includes a failure detection circuit that detects the change of the 1 bit as a parity error.

(4) The logic setting circuit according to any one of (1) to (3), wherein the pull-up or pull-down resistor is formed in the logic circuit section.

(5) The logic setting circuit according to any one of (1) to (4), wherein the pull-up or pull-down resistors are formed by combining resistors having the same resistance value.

As is apparent from the above description, the present invention has the following effects.
(1) Since the effect of insulation failure due to corrosion can be warned in advance, the use of special materials and a highly airtight casing, etc. do not require general countermeasures against corrosion that cause significant cost increase of equipment. .

(2) By devising the resistance value of the pull-up resistor or pull-down resistor included in the logic setting circuit itself, it is possible to realize a diagnosis function for insulation failure without adding an expensive diagnostic circuit that causes an increase in cost.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of a logic setting circuit to which the present invention is applied. The same elements as those of the conventional circuit described with reference to FIG. Hereinafter, the characteristic part of the present invention will be described.

  In FIG. 1, reference numeral 200 denotes a pull-up resistor unit to which the present invention is applied. 201n, 202, 203,... 20n are pull-up resistors connected to the switching means 11, 12, 13,. The feature of the present invention is that the resistance values R1, R2, R3,... Rn of these pull-up resistors are selected to be different from each other such that R1 ≠ R2 ≠ R3 ≠ ... Rn.

  By selecting the resistance value of each pull-up resistor in this way, if an insulation failure occurs under the same conditions between adjacent connection points of the setting switch means connected to the pull-up resistor, it is set in the logic circuit section. The fact that the logical input value with reference to a predetermined threshold voltage changes by 1 bit is used.

  A logic circuit unit 300 to which the present invention is applied includes a failure detection circuit 302 in addition to the same setting reading circuit 301 as the conventional circuit unit. The failure detection circuit 302 detects an insulation failure by using the change of 1 bit as a parity error.

  FIG. 2 is a functional block diagram showing an embodiment for explaining a specific example of failure detection due to insulation failure. In this example, for simplification, the switch means is set to 3 bits at 11, 12, and 13 and the pull-up resistors are three cases of R1, R2, and R3. These pull-up resistors are selected such that R1 ≠ R2 ≠ R3.

  401 and 402 are equivalent resistances representing insulation failure, 401 is connected between signal V1 and signal V2, 402 is connected between signal V2 and signal V3, and it is assumed that insulation failure has occurred under the same conditions. The resistance value is indicated by Rx.

  Here, it is assumed that the setting state by the switch means of the logic setting unit 1 is 1: 0: 1 and the DC potential + V is 3.3V. Conventionally, it is assumed that the pull-up resistors have the same resistance value, for example, R1 = R2 = R3 = 2 kΩ. It is assumed that the impedance between the signal V1 and the signal V2 and between the signal V2 and the signal V3 is lowered due to an insulation failure due to migration or the like, and is short-circuited with an equivalent resistance Rx = 1 kΩ.

  The potential of the signal V2 is 0V. In the conventional circuit, the potential of the signal V1 is 1.1 V because it is divided by R1 (2 kΩ) and Rx (1 kΩ). Similarly, the potential of the signal V3 is 1.1 V because it is divided by R3 (2 kΩ) and Rx (1 kΩ).

  When the threshold voltage set in the logic circuit unit 300 is 1.5 V, the logic circuit unit has a correct logic value V1: V2: V3 = 1: 0: 1, whereas V1: V2: V3 = 0: Read as 0: 0.

  When this logical value change is detected by the failure detection circuit 302 using a widely used parity check technique, the parity check can detect a 1-bit failure but cannot detect a 2-bit failure. That is, in the conventional circuit in which all the pull-up resistors have the same resistance value, failure detection by the parity check method cannot be performed.

  Therefore, in the present invention, the resistance values of adjacent pull-up resistors are changed, for example, R1 = 1 kΩ, R2 = 2 kΩ, and R3 = 3 kΩ. It is assumed that the impedance between the signal V1 and the signal V2 and between the signal V2 and the signal V3 is lowered due to insulation failure due to migration or the like, and the connection is made at Rx = 1 kΩ.

  The potential of the signal V1 is 1.65 V because it is divided by R1 (1 kΩ) and Rx (1 kΩ). Similarly, since the potential of the signal V3 is also divided by R3 (3 kΩ) and Rx (1 kΩ), it becomes 0.825 V.

  Assuming that the threshold voltage set in the logic circuit unit 300 is 1.5 V, the logic circuit unit has a correct logic value V1: V2: V3 = 1: 0: 1, whereas V1: V2: V3 = 1: Read as 0: 0.

  When this logical value change is detected by the failure detection circuit 302 using the parity check method, since 1 bit is changed with respect to the correct logical value, it is possible to detect a failure as a parity error.

  In the embodiment described above, the pull-up resistor is described in the external circuit of the logic unit circuit unit 300. However, the logic circuit unit such as an ASIC may include a group of pull-up resistors having different values. When realizing resistors having different values, a plurality of resistors having the same value may be connected in parallel or in series.

  In the embodiment, the pull-up form is shown in which the common connection point of the setting switch means is connected to the ground potential E, and the resistor group is connected to the DC potential + V. However, the common connection point of the setting switch means is connected to the DC potential + V. However, a pull-down configuration in which the resistor group is connected to the ground potential E may be used.

  In the embodiment, the setting switch means for performing the logic setting is shown in the form of a mechanical contact, but it may be an electronic switch means realized by a semiconductor.

It is a functional block diagram showing an embodiment of a logic setting circuit to which the present invention is applied. It is a functional block diagram which shows embodiment which demonstrates the specific example of the failure detection by an insulation failure. It is a functional block diagram which shows the structural example of the conventional logic setting circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Logic setting part 11, 12, 13, ... 1n Switch means 200 Pull-up resistance part 201,202,203, ... 20n Pull-up resistance 300 Logic circuit part 301 Setting reading circuit 302 Failure detection circuit

Claims (5)

In the logic setting circuit for inputting the voltages at the connection points of a plurality of logic setting switch means connected to different pull-up resistors or pull-down resistors to the logic circuit section,
A logic setting circuit, wherein the pull-up resistor or the pull-down resistor has different resistance values.   When an insulation failure occurs under the same conditions between the adjacent connection points of the logic setting switch means, the logic input of the logic setting switch means with reference to a predetermined threshold voltage set in the logic circuit section 2. The logic setting circuit according to claim 1, wherein the pull-up resistor or the pull-down resistor has a different resistance value so that the value changes by 1 bit.   The logic setting circuit according to claim 2, wherein the logic circuit unit includes a failure detection circuit that detects a change in the 1 bit as a parity error.   4. The logic setting circuit according to claim 1, wherein the pull-up or pull-down resistor is formed in the logic circuit unit. 5. The logic setting circuit according to claim 1, wherein the pull-up or pull-down resistor is formed by combining resistors having the same resistance value.

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