JPS63156422A - Two-way input/output circuit - Google Patents

Abstract

PURPOSE:To prevent a data input/output line from being set at high impedance, by connecting a pull-up resistor or a pull-down resistor to the data input/output line by using a switching device ON/OFF-controlled by a control signal which sets an output gate at a deabled state. CONSTITUTION:Plural two-way input/output circuits are connected to a data bus 30, and the input of data from the data bus 30 and the output of the data to the data bus 30 are performed at need. At the time of inputting the data, only an input gate is operated, and the output gate is set at the desabled state (high impedance state). Adversely, at the time of outputting the data, only one output gate is selected, and other output gates are set at the disabled states. Thus, since pull-up is performed by a FET at the time of desabling all of the output gates, it is possible to prevent the data bus 30 from being set at an undesirable state such as the high imedance state.

Description

[Detailed Description of the Invention] [Summary] In order to prevent the data input/output line, which is a bidirectional input/output circuit and is shared by an output gate and an input gate, from going into a high impedance state, the output gate is set to high. The data input/output line is pulled up or pulled down with a signal that makes it impedance.

[Industrial Field of Application] The present invention relates to a bidirectional input/output circuit, and more particularly to a bidirectional input/output circuit that can prevent data input/output lines from entering a high impedance state.

In the data input/output circuit, a bidirectional input/output circuit using 0MO8-LSI is used.

The 0MO8-LSI was originally developed with the aim of reducing the power consumption of the circuit, but since it uses high impedance circuit elements, it is often destroyed by static electricity. It is desired to realize a bidirectional input/output circuit that takes advantage of the advantages and does not cause damage.

[Prior Art] FIG. 3 is a diagram showing one line of a bidirectional input/output circuit using 0MO3. In the figure, 1 is an output gate for data output having a three-state state whose output is controlled by a control signal, and 2 is an input gate for data input.

3 is a data input/output line to which the output gate 1 and the input gate 2 are commonly connected. In an actual bidirectional bus circuit, a plurality of such bidirectional input/output circuits (for example, 8, 16°, 32, etc.) are assembled.

In FIG. 3, when outputting data, the output gate 1 is enabled by a control signal, and then data is output onto the input/output line 3. Next, at the time of data input, after the output gate 1 is put into a disabled state (high impedance state g!A) by a control signal, the data on the input/output line 3 is taken in from the input gate 2.

[Problems to be Solved by the Invention] However, in a bidirectional input/output circuit using 0MO8, when the data input/output line 3 becomes a high impedance state,
Excessive threshold current may occur, leading to device destruction. In a bidirectional bus circuit made up of a large number of bidirectional input/output circuits as shown in Figure 3, a state where the data input/output line (data bus) becomes high impedance always occurs, so the A pull-up method or a pull-down method as shown in FIG. 5 is adopted.

Figure 4 shows resistor 1o connected to data input/output line 3 and power supply vC.
A case where the resistor 10 is connected between the C lines is shown, and FIG. 5 shows a case where the resistor 10 is connected between the data input/output line 3 and the ground. In either case, the impedance 10 is usually realized using an external resistor.

However, in both the pull-up and pull-down methods, current flows when the output gate 1 is enabled. In the case of FIG. 4, a current of 10L flows from the pull-up resistor 10 toward the output gate 1,
In the case of Figure 5, from output gate 1 to pull-down resistor 1
A current 108 begins to flow toward zero. The generation of such current consumes a large amount of power when many bidirectional inputs and outputs are formed in the same package, such as in LSI, and the advantage of low power consumption, which is a feature of 0MO8, is lost. It will be lost.

For example, if we assume that the resistance value of resistor 10 is 10Ω,
Each bus consumes 0.511 IA of current. If this becomes 20 buses, the pull-up/pull-down resistors alone will consume 1 (lA) of current.

The present invention has been made in view of these points, and
It is an object of the present invention to provide a bidirectional input/output circuit that can reduce power consumption without bringing a data input/output line (pass line) into a zero impedance state.

[Means for Solving the Problems] FIG. 1 is a circuit diagram of the principle of the present invention. Components that are the same as those in FIG. 3 are designated by the same reference numerals. The difference between the conventional circuit shown in FIG. The point is that it is turned on and off by a control signal.

[Function] When the output gate 1 is set to a high impedance state by a control signal, the switch element 22 is set to a high impedance state by the same control signal.
Turn on. As a result, the data input/output line 3 is pulled up by the resistor 21 and does not enter a high impedance state. Moreover, when the output gate 1 is enabled (well, since the switch element 22 is turned off, there is no current consumption through the resistor 21. Therefore, it is also possible to reduce power consumption.

[Embodiment] FIG. 2 is a configuration diagram showing an embodiment of the present invention. Although the illustrated embodiment uses an FET as the switching element, other switching elements such as transistors may be used. As shown in the figure, a plurality of internal input/output circuits are connected to one data bus 30, and input data from the data bus 30 and output data to the data bus 30 as necessary. In this case, when data is input, only the input gate operates, and the output gate is in a disabled state (high impedance state). Therefore, the FET is on at this time.

Conversely, when outputting data, only one output gate is selected and the other output gates are disabled. Therefore, in this case, only the selected output gate is enabled and the FET is turned off, while the other output gates are disabled and the FET is turned on and pulled up. In this way, according to the present invention, all output gates are pulled up by the FETs when disabled, so the problem that the data bus 30 goes into a high impedance state does not occur. Moreover, the data input/output line is pulled up by the resistor only when the output gate is in high impedance, and is not pulled up by the resistor in other cases, so that power consumption can be reduced.

In the above embodiment, the case where a pull-up resistor is connected between the power supply line and the data input/output line is explained as an example, but it is also possible to connect a resistor between the data input/output line and the ground via a switch element. good. A similar reduction in power consumption can be achieved, and the occurrence of a high impedance state in the data input/output line can also be prevented.

[Effects of the Invention] As described above in detail, according to the present invention, a pull-up resistor or To provide a bidirectional input/output circuit that can prevent a data input/output line (pass line) from becoming high impedance by connecting a pull-down resistor to the data input/output line, and also achieves low power consumption. be able to.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the principle of the present invention, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a diagram showing a conventional example of a bidirectional input/output circuit, and Fig. 4 is a diagram of a pull-up type circuit. Explanatory diagram: FIG. 5 is an explanatory diagram of the pull-down method. In FIG. 1, 1 is an output gate, 2 is an input gate, 3 is a data input/output line, 21 is a resistor, and 22 is a switch element. ■℃ 11 Output gate 2 - Input gate 3 Data input/output line 21, Resistor 22

Claims (1)

[Claims] An output gate (1) that is a gate that can take three states and outputs data to a data input/output line (3), and an input that inputs data from the data input/output line (3). A switch connected between the gate (2) and the data input/output line (3) and the power supply line or ground via a pull-up or pull-down means (21) and controlled on/off by the control signal of the output gate (1). A bidirectional input/output circuit composed of an element (22).