The second chapter is the foundation and application of combinational logic circuits.

Integrated logic gate circuit

TTL and non-logic gate CMOS gate circuit

Interface circuit between TTL and CMOS

Fundamentals of combinational logic circuits

Combinatorial logic circuit analysis

Design of combinational logic circuit

Common combinational logic circuits

viper

An adder is a device that generates the sum of numbers. Complement and addend are inputs, and the devices for addition and carry are half adders. If you input addend, addend and low-order decimals, and output sum and carry, it is a full adder. It is usually used as an arithmetic and logical part of a computer to perform logical operations, shifts and instruction calls. In electronics, an adder is a digital circuit that can add numbers. In modern computers, adders exist in arithmetic logic units (ALU). Adders can be used to represent various numerical values, such as BCD, plus three codes, and the main adder operates in binary. Since negative numbers can be represented by two's complement, there is no need to add or subtract.

Adders are used for addition.

It is a device that generates the sum of numbers. Complement and addend are inputs, and the devices for addition and carry are half adders. If you input addend, addend and low-order decimals, and output sum and carry, it is a full adder. It is usually used as an arithmetic and logical part of a computer to perform logical operations, shifts and instruction calls.

For the binary addition of 1 bit, there are five related quantities: 1, addend A, 2, addend B, 3, the carry CIN of the previous bit, 4, the sum of the added two bits, S, 5, and the carry COUT generated by the addition of two bits. The first three quantities are input quantities, the last two quantities are output quantities, and all five quantities are 1 bit.

For 32-bit binary addition, there are also five related quantities: 1, addend A(32 bits), 2, addend B(32 bits), 3, the carry CIN of the previous bit (1bit), 4, the sum of these two digits S(32 bits), 5, standard.

To realize 32-bit binary addition, a natural idea is to repeat the binary addition of 1 bit for 32 times (that is, a bit-by-bit carry adder). This is undoubtedly feasible and easy to do, but because the CIN of each bit is provided by the COUT of the previous bit, the calculation of the second bit can only begin after the result is calculated by 1 bit; The third place must first calculate the result of the second place before starting to calculate, and so on. Only after all the results have been calculated in the first 3 1 bits can the last 32 bits be calculated. In this way, it takes 32 times as long to realize 32-bit binary addition as 1 bit binary addition.

encoder

An encoder is a device that compiles signals (such as bit streams) or data and converts them into signal forms that can be used for communication, transmission and storage. The encoder converts angular displacement or linear displacement into electrical signals, the former is called code wheel, and the latter is called code wheel. According to the reading mode, encoders can be divided into contact type and non-contact type; According to the working principle, encoders can be divided into incremental and absolute types. Incremental encoder converts displacement into periodic electrical signal, and then converts this electrical signal into counting pulses, and the number of pulses indicates displacement. Each position of absolute encoder corresponds to a certain digital code, so its indication value is only related to the starting and ending positions of measurement, and has nothing to do with the intermediate process of measurement.

Encoders can be classified in the following ways.

1, according to the different classification of codewheel.

(1) Incremental formula: that is, every unit angle is rotated, a pulse signal is sent (sine and cosine signals are also sent,

Then it is subdivided and chopped into pulses with higher frequency), which are usually output by phase A, phase B and phase Z. Phase A and phase B are pulse outputs with a mutual delay of 1/4 cycles. According to the delay relationship, forward and reverse can be distinguished, and the second or fourth frequency multiplication can be carried out by taking the rising edge and falling edge of phase A and phase B; Z-phase is a single-cycle pulse, that is, one pulse is emitted every cycle.

(2) Absolute value type: corresponding to a circle, each reference angle sends out a unique binary value of the corresponding angle, and multiple positions can be recorded and measured by an external circle recording device.

2. According to the signal output type, it can be divided into voltage output, open collector output, push-pull complementary output and long-line drive output.

3, according to the encoder mechanical installation form classification

(1) axial type: axial type can be divided into clamping flange type, synchronous flange type and servo installation type.

(2) Casing type: Casing type can be divided into half-empty type, full-empty type and large-caliber type.

4. According to the working principle of the encoder, it can be divided into photoelectric type, magnetoelectric type and touch brush type.

translator

Decoder is an important device of combinational logic circuit, which can be divided into variable decoding and display decoding. Variable decoding is generally a device with less input and more output, which is generally divided into 2n decoding and 842 1BCD decoding. Display decoding mainly solves the conversion function of displaying binary numbers to corresponding decimal or hexadecimal numbers. Generally divided into two categories: driving LED and driving LCD.

Data selector and data distributor

digital comparator

Competitive Adventure in Combinatorial Logic Circuits

Summary of this chapter

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