JPS61176867A - Terminal resistance checking circuit for ttl level interface - Google Patents

Abstract

PURPOSE:To make the easy checking of the packaging state of terminal resistors possible by providing the resistors between signal wires to which the terminal resistors are connected and earth and checking the voltage at both terminals of the resistors by utilizing the threshold level of an IC. CONSTITUTION:A controller A and a floppy disk device B are connected by the signal wires 1 and the terminal resistors 2 are connected between the wires 1 and a +5V power source as part of a TTL level interface. A check circuit C is connected to the wires 1 and resistors 4 having the same resistance value as the resistance value of the resistors 2 are connected between the wires 1 and the earth. The voltage at both terminals of the resistors 4 is inputted to a multiinput NOR gate IC 5. A logic 1 is outputted from the controller A to the wires 1 as a check signal, then if all the resistors 2 are normally connected to the +5V power source, the +5V is divided down to a half and the voltage at the wires 1 is +2.5V. Since the threshold voltage of the TTL level IC is about 1.4V, the output terminal 6 of an NOR gate IC 5 is a logic 0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for checking for an abnormality in the resistance value or disconnection of a terminating resistor for pulling up to the TTL level in a TTL level interface circuit.

[Conventional technology]

FIG. 3 shows a conventional termination resistance check circuit for a TTL level interface. The part surrounded by a broken line A is a controller, and the part surrounded by a broken line B, for example, a floppy disk device, is controlled via a signal line 1. A terminating resistor 2 is connected between the signal line 1 and the +5V power supply, and a voltmeter 31 is connected between the signal line 1 and the ground, or a voltmeter 32 is connected between both ends of the terminating resistor 2.

In this figure, when controlling a floppy disk as a device, for example, the control signal from controller A is T.
In the case of TL level, when the logic is “1”, it is definitely the logic “1”.
”, logic “0” - to ensure logic “0”, signal line 1 and +5V are generally connected as part of the TTL level interface circuit in each floppy disk drive.
A terminating resistor 2 is connected between the power supplies to pull up the signal line 1. However, sometimes the signal line 1 is not pulled-amplified due to a defect in the manufacturing process such as a poor connection of the terminating resistor 2 or a broken pattern on the printed circuit board.

In order to discover this defect, conventionally a voltmeter 31 was placed between the signal line 1 and the ground, or a voltmeter 31 was placed between both ends of the terminating resistor 2.
2 was connected, and from the indicated value it was discovered that the termination resistor 2 had a poor connection or a broken pattern. In other words, under normal conditions, when the control signal is logic "1", the voltmeter 31 outputs 5V;
The voltmeter 32 indicates Ov, and conversely, when the logic is "0", the voltmeter 31 indicates 0■, and the voltmeter 32 indicates 5■. However, if there is a malfunction such as a poor connection or a broken pattern, the voltmeter 31
Alternatively, the indicated value of 32 becomes uncertain, and an abnormality in the circuit can be discovered.

[Problem that the invention aims to solve]

In this way, the conventional TTL level interface termination resistance check circuit uses a voltmeter to measure the voltage of the signal line, so it requires a measuring device such as a digital voltmeter, and it also requires a measuring device such as a floppy disk device. Checking devices one by one, which are produced in large quantities, requires a great deal of effort and is inefficient.

Furthermore, the resistance value of the terminating resistor is set depending on the IC used, etc., but although conventional check circuits can check for disconnections such as poor connections and broken patterns, they cannot check for abnormalities in the resistance value. However, the resistance values of recent resistors are displayed using color codes rather than numbers, which can lead to misuse, and in such cases it is necessary to discover abnormalities in the resistance values.

The technical problem of the present invention is to solve such problems in conventional TTL level interface termination resistance check circuits, and to easily and automatically check the termination resistance mounting state within a short time using a simple circuit configuration. The goal is to make it possible.

[Means for solving problems]

The technical means of the present invention taken to solve this problem is to connect the signal end of the pull-up terminating resistor of the TTL level interface to each input end of a gate circuit consisting of an IC, and to A resistor is provided between the ground, and when the voltage input to the gate circuit from both ends of the resistor falls below the threshold voltage of the IC, the output of the gate circuit is inverted to notify an abnormality.

In addition, the signal end of the pull-up terminating resistor of the TTL level interface is connected to the comparison input end of each of the two comparators, and a resistor is provided between the signal end and the ground, and one of the two comparators is connected to the allowable voltage. One voltage is set at the upper limit of the range, and the other is set at the lower limit of the allowable voltage range, and the output end of each comparator is connected to the input end of a gate circuit composed of an IC.

[Effect]

According to this technical means, by connecting a resistor with approximately the same resistance value as the terminating resistor between the signal line to which the terminating resistor is connected and the ground, the signal line should be logically "1". However, if the terminating resistor is not connected and pulled up, the potential of the signal line will be pulled to the ground side via the resistance between ground and becomes logic "0". Therefore, this signal is NOR'ed. If the input signal is an input signal of a gate or a NAND gate, the output signal of the gate circuit becomes logic "1", indicating that a failure such as a poor connection of a terminating resistor has occurred in one of the input signals. When the terminating resistor is connected, the potential of the signal line becomes logic "1", so the output signal of the gate circuit is inverted and becomes logic "0", indicating that there is no abnormality.

In addition, the signal end of the pull amplifier termination resistor is connected to the comparison input end of each of the two comparators, and a resistor is provided between the signal end and the ground, so that one of the two comparators is connected to the upper limit of the allowable voltage range. By setting the output terminal of each comparator to the input terminal of the gate circuit consisting of an IC with the other set to the lower limit of the allowable voltage range, abnormalities in the resistance value of the terminating resistor can be prevented. Can be discovered. In other words, in normal conditions, the signal line is
When set to 1", the potential of the signal line becomes a value divided by the terminating resistor and the resistor installed between the signal line and the ground. Therefore, the potential of the signal line, that is, the voltage across the resistor between the ground and the ground, is ,
It is input to two comparators for upper limit detection and lower limit detection, and when the voltage is higher than the upper limit voltage or lower than the lower limit voltage, a logic "0" is output to the gate circuit, and the abnormal signal is output from the gate circuit as a logic "1". Output. Therefore, by comparing the voltage that occurs when a normal terminating resistor is used with the upper and lower voltage limits, including the tolerance of the terminating resistor, it is possible to determine whether the value of the terminating resistor is abnormal, in addition to poor connections or broken patterns. It can also detect things.

〔Example〕

Next, how the termination resistance check circuit for a TTL level interface according to the present invention is actually implemented will be explained using an example. FIG. 1 is a circuit diagram showing an embodiment of a termination resistance check circuit for a TTL level interface according to the present invention.

The parts surrounded by broken lines A and B in this figure are a controller and, for example, a floppy disk device, and are connected by a signal line 1, and the signal line 1 and +
A terminating resistor 2 is connected between the 5V power supplies. A check circuit C according to the present invention surrounded by a broken line is connected to this signal line 1, a resistor 4 is connected between the signal line 1 and the ground, and the voltage across this resistor 4 is input to a multi-input NOR gate IC5. be done.

TT transmits device selection signals, motor control signals, write data, etc. from controller A to device B via signal line 1.
Outputs at L level, but logic “L” or logic “0”
As part of the TTL level interface within device B, signal lines 1 and +5V are
A terminating resistor 2 is connected between the power supplies and pulls up the signal line 1. However, if the termination resistor 2 is not connected properly due to a cut in the printed circuit board pattern, etc.
TL level signal transmission is not performed accurately, resulting in malfunction.

Therefore, when the controller A outputs logic "1" to the signal line 1 as a check signal for the terminating resistor 2, the terminating resistor 2 is now normally connected to the +5V power supply and the signal line 1, and the resistor 4
If the resistance value is the same as that of terminating resistor 2, signal line 1 is +5
v is divided by half, resulting in +2.5V. TTL
In a level IC, the threshold voltage for logic "1" or logic "0" is approximately 1.4V, so the signal line 1
becomes logic "l", therefore, connect the terminal resistors 2 of multiple floppy disk devices in the same way,
By inputting the voltages across the resistor 4 to the NOR gate IC5 (which has multiple input terminals), the NOR gate I
C5 has an output terminal 6 of logic 60 only when all its input signals are logic "1", so it is a NOR gate IC.
When the output terminal 6 of the device B is logic "0", it can be said that all the terminal resistors 2 of the device B are connected normally.

On the other hand, if the terminating resistor 2 is not properly connected, the signal line 1 is connected to the logic "O" via the resistor 4 even though the controller A outputs a logic "L" check signal.
get caught up in If even one of the input signals of the NOR gate IC5 becomes a logic "O", the output signal 6 becomes a logic "1", so when the output terminal 6 of the NOR gate IC5 is a logic "1", the device This indicates that there is an abnormality in the connection of one of the terminating resistors 2 of B.

Further, as shown in FIG. 2, a signal is guided from the signal line 1 to a check circuit, and a variable resistor 7 is provided between the signal line 1 and the ground. The voltage across the variable resistor 7 is input to the phase input terminal a of the comparator 8 and the difference input terminal S of the comparator 9, and the output signal lines 11 and 12 of these comparators 8 and 9 are connected to the input terminal of the NOR gate IC 10. . Now, hypothetically,
Assuming that the specified value of the terminating resistor 2 is αΩ, and the resistance value of the variable resistor 7 is also adjusted to αΩ, when a logic “1” is output from the controller A to the signal line 1 as a check signal, the potential of the signal line 1, that is, the variable The voltage across the resistor 70 is +5V
is divided by the terminating resistor 2 and variable resistor 7, resulting in +2.5V. If the resistance value αΩ of the terminating resistor 2 is allowed to have an error of ±8% and is in the range of 0.92α to 1.08α, the voltage across the variable resistor 7 will also be in the range of 2.6v to 2.4v. Therefore, the voltage 2.6■ corresponding to the lowest limit value 0.92αΩ of the terminating resistor 2 is set at the difference input terminal C of the comparator 8 by adjusting the variable resistor 13 (and the phase input terminal of the comparator 8). As long as the voltage of a does not exceed 2.6V, its output signal line 11 becomes logic "1".Also, the variable resistor 7 corresponding to the maximum limit value of 1.02αΩ of the terminating resistor 2
By adjusting the variable resistor 14 and setting the voltage 2.4V across the voltage at the phase input terminal d of the comparator 9, the output signal of Line 12 becomes a logic "1". Therefore, when the terminating resistor 2 is properly connected and its resistance value is within the allowable value, the output signal line 11.1 of the comparator 8.9
2 becomes logic "1". These output signal lines IL12
are respectively connected to the input terminal eSf of the NOR gate ICl0.

This combination of variable resistor 7 and pair of comparators 8.9 is wired in parallel to check the termination resistance of other devices in the same way, and the output of each comparator is connected to NO.
By inputting it to the other input terminal of the R gate ICl0, it becomes NO when all the termination resistors 2 are properly connected.
R game) All the input terminals of ICIO become logic "1", the output terminal 15 of said ICl0 becomes logic "O", and the resistance value of terminating resistor 2 is inappropriate and is smaller than the minimum limit value 0.92αΩ In this case, the voltage at the phase input terminal a of the comparator 8 exceeds 2.6V, and the output signal of the comparator 8 becomes logic "O", or conversely, the resistance value of the terminating resistor 2 increases due to pattern breakage, etc. If it is larger than the maximum limit value 1°08αΩ, the voltage at the differential input terminal of the comparator 9 becomes smaller than 2.4V, and the output signal of the comparator 9 becomes logic “0”.

Therefore, the output terminal 15 of ICIO (NOR game) is logic "1"
This indicates that an abnormality has occurred in one of the terminating resistors. A similar effect can be achieved by using a NAND gate in place of the NOR gate 5.10.

〔Effect of the invention〕

As described above, according to the present invention, in order to check the terminal resistance of a TTL level interface, a resistor is provided between the signal line and the ground, and the voltage across the resistor is checked using the threshold level of the IC of the gate circuit. Therefore, regardless of the resistance value of the terminating resistor, simply determining whether or not it is connected can be realized at low cost with a very simple circuit configuration. Additionally, since no measuring instruments are required, checks can be performed easily and quickly, and automation is also possible.

Furthermore, the voltage across the resistor placed between the signal line and the ground is
By checking the range using two comparators, it is possible to check the error in the resistance value of the terminating resistor without using a measuring device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a termination resistance check circuit for a TTL level interface according to the present invention, FIG. 2 is a diagram showing another embodiment of the circuit of the present invention, and FIG. 3 is a diagram showing a conventional termination resistance check circuit for a TTL level interface. FIG. 3 is a diagram showing a check circuit. In the figure, 1 is a signal line, 2 is a terminating resistor, 31.32 is a voltmeter, 4 is a resistor, 5 and 10 are NOR gates) IC17 is a variable resistor, and 8.9 is a comparator. Patent Applicant: Fujitsu Limited Representative, Patent Attorney Minoru Aoyagi Figure 1 History of Honsakuro Example 2

Claims (2)

[Claims] (1) Connect the signal end of the pull-up termination resistor of the TTL level interface to each input end of the gate circuit consisting of an IC, and provide a resistor between the signal end and the ground, and connect the gate circuit from both ends of the resistor. A terminal resistance check circuit for a TTL level interface, characterized in that the circuit is configured to invert the output of the gate circuit when the input voltage drops below the threshold voltage of an IC. (2) The signal end of the pull-up termination resistor of the TTL level interface is connected to the comparison input end of each of the two comparators, and a resistor is provided between the signal end and the ground, and one of the two comparators The TTL is characterized in that one comparator is set at the upper limit of the allowable voltage range, the other is set at the lower limit of the allowable voltage range, and the output end of each comparator is connected to the respective input end of a gate circuit consisting of an IC. Termination resistance check circuit for level interface.