软硬件系统编程PPT (16).pdf
触发器与加法器触发器与加法器 Flip-flop and Adder Logic circuit Logic circuit,based on binary,is a circuit consisting various logic gates to make digital signal logical operation Combinational logic circuit output at any time depends only on its input,and has nothing to do with the previous state of circuit(without memory function)Sequential logic circuit output at any time depends on its input as well as the previous state of circuit(with memory function)2 3 1.1.Flip-flop Flip-flop is a logic circuit constructed by basic logic circuit and it has memory function belonging to sequential logic circuit Power on：it can output a high level or a low level when trigger signal occurs,the output state will invert from high level to low level/from low level to high level If the signal of flip-flop is invalid,the output state will remain the same until the new signal occurs or power off Q Q 1 0 0 1 X X-RS Flip-flop 4&SRQQG1G2Flip-flop S R 0 1 1 0 1 1 0 0 Two stable states Input output Now allow Logic truth table of RS flip-flop The state remains the same RS flip-flop has independent logic function and can exist independently After encapsulation,it can be represented by a symbol 5 Flip-flop SRQQSR&SRQQG1G2Terminal 1(SET)Terminal 0(RST)abstraction&QQ&G1G2G3G4CPDAdding two NAND gates on the RS flip-flop Flip-flop Control site Input terminal Output terminal 0 1 DCPQQD flip-flop The logic symbol of D flip-flop CP=0,output state remains the same CP=1,output depends on the state of terminal D when the power is on,the output of the flip flop will always remain in a certain state remaining at“1”or“0”flip flop can store a bit 0 or a bit 1 at output terminal flip flop is a logic device with memory function 7 Flip-flop 8 The function of flip-flop flip flop is a logic device with memory function output terminal will always remain in a certain and stable state at any time(0 or 1)a flip-flop can store 1-bit binary number for example：8 D flip flop can store 8-bit binary numbers 10110110 Internal memory 2.Adder Microprocessor consists of three parts:controller,arithmetic unit and register All programs are executed in the arithmetic unit The core of arithmetic unit is arithmetic logic unit(ALU),which is constituted by various logic gates.The main functions are as follow：binary arithmetic operations,logic operations and other operations A Athe basic function of ALU is arithmetic operation 9 In modern computers：by introducing complement,subtraction can be converted into addition multiplication can be converted into shift and addition division can be converted into shift and subtraction which can be converted into addition Addition is the most basic operation 10 Adder The basic function unit of ALU is adder Adder Half adder To perform addition of two 1-bit binary numbers,and carry will not be passed for addition to successive bits Input：addend,augend Output：sum,carry Full adder To perform addition of two 1-bit binary numbers,and carry will be passed for addition to successive bits Input：Addend,augend,carry from low order Output：Sum,carry 11 Half adder S S=A A B B C C=A AB B 12 Logical relation of half adder A B S C 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1&=1 A B S C Adder Input Output Carry Full adder is constituted by two half adders and a OR gate 13 Adder Input Input A A B B C Cinin S S C Coutout 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 AB&1=1=1SC0Ci0 1 0 0 1 1 0 0 0 1 1 0 1 1 1 0 AB&=1=1SC0CiAnother adder circuits Full adder is a logic unit with complete functions 14 Adder with same logic function but can constitute different circuits Cin Cout A Ai i B Bi i C Ci i-1 1 C Ci i S Si i Logic symbol numerous 1-bit full adders can constitute numerous-bit adders Adder C2C3S01位全加器A2B2C41位全加器C11位全加器C01位全加器A0B0A1B1S1S2A3B3S34-bit ripple-carry adder 1-bit full adder 1-bit full adder 1-bit full adder 1-bit full adder
