Design a Logic Circuit Using Tri-state Gates

Three-state gate in digital circuit
can refer to another blogDigital circuit basics-CMOS gate circuit (NAND gate, NOR gate, NOR gate, OD gate, transmission gate, tri-state gate)

In addition to the high and low levels of the tri-state gate, there is a third state-high impedance state.
Three-state gate (Three-state gate) is an importantBus interface circuit. Also often appear on the pins of the chip, in When designing DFT/Boundary scan Need to understand several forms of chip pin feet, including three-state output

1. Tri-state gates are commonly used at the output of ICs,The output and input are the same as the output buffer; the output and input reversed are called the output buffer

2. Tristate refers to its outputIt can be a general binary logic circuit, That is normal high level (logic 1) or low level (logic 0),And can maintain the unique high impedance state. The high resistance state is equivalent to the cut-off state (large resistance, equivalent to an open circuit).

3. The high-impedance state is a common term in a digital circuit, which refers to an output state of the circuit, which is neither a high level nor a low level. If the high-impedance state is input to the next level circuit, there is no The impact is the same as not connected. If it is measured with a multimeter, it may be high or low, depending on what is connected behind it.

4. When in the high impedance state, the output resistance is very large, which is equivalent to an open circuit, without any logic control function. The significance of the high resistance state is that it is impossible to break the circuit in the actual circuit. The control of the output logic state of the three-state circuit is realized through an input pin.

5. The three-state gate has an EN control enable terminal to control the on and off of the gate circuit. Devices that can have these three states are called tri-state devices.When EN is valid, the tri-state circuit presents a normal "0" or "1" output; when EN is invalid, the tri-state circuit gives a high-impedance state output.
   

6. When the tri-state gate is used in the bidirectional port, as shown in Figure 1, set Z as the control item. When Z=1, the tri-state gate is in a high-impedance state, and the above line is unavailable for input only. When Z=0, The tri-state gate is in the normal high and low level output state, and can be output, that is, O pass. A tri-state gate is an output stage with extended logic functions and a control switch.Mainly used for bus connection, because the bus only allows one user at a time. There are usually multiple devices connected to the data bus, and each device is gated by signals such as OE/CE. If the device is not gated, it is in a high-impedance state, which is equivalent to not being connected to the bus and does not affect the work of other devices.
   

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Design a Logic Circuit Using Tri-state Gates

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