SU900260A2 - Device for checking digital circuits - Google Patents

Description

The invention relates to automation and computing and can be used to visually monitor and indicate the levels of logic signals.

According to the main author. St. No. 788077, a device for controlling digital circuits is known, comprising a valve and a current limiting resistor connected to the first indicator input, and an emitter follower, an output connected to the input of the first valve, and an input to the input of the second valve whose output is connected to the second input of the indicator and the inputs of the third and fourth valves. The outputs of the first and third valves are connected and connected to the third and fourth inputs of the indicator, and the output of the fourth valve is connected to the remaining inputs of the indicator 1.

A disadvantage of the known device is that the Free Input and Open State conditions are indicated in the same way, which leads to ambiguity of control and makes it difficult for the operator to work.

In addition, when monitoring the state of Logic zero, the controlled valve is additionally loaded by the outgoing current of one of the device's valves, which limits its use when working with low-power TTL circuits, since it causes overloading.

The purpose of the invention is to expand the functionality of the device, i.e. additional distinction and display of the Free Input state while reducing the influence of the device on the controlled circuit.

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This goal is achieved in that the device contains second and third emitter followers, fifth and sixth valves and a bias resistor, the input of the second emitter follower is connected to the input of the first emitter repeater and through the bias resistor with a common bus, and the output is connected to the input of the second valve through the third emitter follower - to the input of the sixth valve, the output of which is connected to one input of the fifth valve, the other inputs of which are connected to the outputs of the third and fourth valves, respectively, and the output to one th inputs of the indicator.

FIG. 1 schematically shows the proposed device; in fig. 2 type of indication of all monitored conditions.

The device contains the first emitter follower 1, the first 2, the second 3, the third 4 and the fourth 5 fans, the indicator 6, the current limiting resistor 7, the second 8 and the third 9 emitter repeaters, the fifth 10 and 11 connected valves, the bias resistor 12 and the input bus of the device 13.

The device works as follows.

Breakage

In the state

when the input bus 13 is not in contact with the control point, the voltage across it is determined by the current flowing through the resistor 12 and is set to + 1V. In this case, the voltage at the output of the repeater 1 is equal to the difference between the input voltage and the voltage drop at the pn junction transistor V, i.e. 1-0, 3 V. This voltage is less than the voltage Un of the response threshold of all integral TTL valves which is 1-4V.

The voltage at the output of the repeater 8 is equal to the sum of the input voltage and the voltage drop at the p-junction of the transistor Vj, i.e. 1 + 0.7 - 1.7 V This voltage is greater than иif, so the output of the valve 3 is a logical zero and the valves 4 and 5 are closed. Since the valves 2 and 4, the outputs of which are combined according to the Wired OR closed circuit, then. On bus 14, the high level and the ct and -b segments of the indicator b are not luminous.

Since the output of the closed ventilation 5 is high, the segments c, d e and e are also not illuminated.

The voltage at the output of the emitter follower 9 is equal to the voltage on the bus 13, since, going 0.7V at the emitter of the transistor Vj, it decreases by 0.7V at the emitter of the transistor Vj. Due to the condition of the Open state, the input voltage is less than U, the valve 11 is closed. Therefore, all three inputs of the valve 10 are high and it is open, which causes the g segment of the indicator 6 to glow (Fig. 2).

If the voltage on bus 13 is equal to 2.4 V, (the lower limit of the logical unit), then the voltage at the output ps of the repeater 1 is 2.4-0,, 7 V, t. Is greater than U) - ,.

Consequently, the valve 2 is open and the light of the mc segments a and b of the indicator 6. The remaining segments of the indicator b are not light TCs, since the voltage at the output of the emitter follower 8 is 2, 4-t-O, 7 3.1 V, i.e. more Ut, H valve 3 is open, which causes closing of the valve 5. The valve 10 is also closed with a logic zero from the output of the valve 2.

If the voltage on bus 13 is equal to 0.4V (the upper limit of Logic zero), then the voltage at the output of repeater 8 is 0.4 + 0,, 16, which is less than U, and valve 3 is closed. At the same time, both valves 2 and 4 are open, and the segments of the o-, -fe, c, d, e and indicator 6 are light. At the same time, the valve 10 is closed and the g segment is not illuminated.

If rectangular pulses arrive at the input of the device, the device alternately is in the state J | o that you have failed

Discontinuous illumination of segments a and S and flashing of segments c, d, e and with the frequency of external generation (Fig. 2).

If the input bus 13 of the device is in contact with the free input of a TTL valve having a potential of 1.6 V, then due to the high input resistance of the device, the potential of the bus 13 becomes equal to 1.6 V (instead of 1 OV in the Open state).

The voltage at the output of repeater 1 will be 1.6-0,, 9 V, which is less and the valve 2 is closed. The output at the output of the repeater 8 is 1.6 + 0.7 2.3 V, which is greater than Uv ,, and the valve 3 is open, and the valves 4 and 5 are closed. Segments o, & , c, d, 6 and | indicator 6 - extinguished. The output voltage of the repeater is 9 1.6 b, which is higher than Uy ,. As a result, the valve 11 is open and the valve 10 is closed, therefore, in contrast to the condition of the Open circuit, the Free input state does not light up and the g segment of the indicator 6.

Thus, the proposed device allows unambiguously to indicate five states at the outputs of the TTL microchips, instead of four, of the known ones. In addition, due to the high input impedance, the input currents of the device in the control modes of both the logical unit and the logical zero do not exceed 50 µA. (The base currents of the transistors V and f. This allows you to expand the functionality of the device and allows you to more effectively use it while monitoring the logical states of digital devices, including those built on low-power TTL and CMOS integrated circuits.

Claims (1)

Invention Formula Device for controlling digital circuits according to ed. St. No. 788077, characterized in that, in order to expand the functionality of the device, it comprises the second and third emitter followers, the fifth and sixth valves and the bias resistor, with the input of the second emitter repeater connected to the input of the first emitter follower and through a common bias resistor