Unit5 Combinational circuit and instrumentation system

3 One-bit Half Adder: One-bit Full Adder: Adding Two One-bit Operands Sum = A  B  Cin Cout = A.B + B.Cin + A.Cin FA AB C in C out Sum Sum = A  B Cout = A.B HA AB C out Sum A B Sum Cout C in A B Sum Cout

4 N-Bit Ripple-Carry Adder: Series of FA Cells To add two n-bit numbers C0C0 FA A0A0 S0S0 B0B0 A1A1 S1S1 B1B1 A2A2 S2S2 B2B2 A n-1 S n-1 B n-1 CnCn... Note: adder delay = Tc * n Tc = (C in :C out delay) FA AB CinCin C ou t Sum

5 4-bit Ripple Carry Addition: Example C0C0 FA A0A0 S0S0 B0B0 A1A1 S1S1 B1B1 A2A2 S2S2 B2B2 A3A3 S3S3 B3B3 C4C4 C1C1 C2C2 C3C3 T= T=0 B=0101 A=0011 S=0000 S= T=2 S= T=3 S= T=4 S=1000

Carry look ahead adder

9 MULTIPLEXERS (Data Selectors) A multiplexers (MUX) is a device that allows digital information from several sources to be routed onto a single line for transmission over that line to a common destination. The basic multiplexers has several data input lines and a single output line. It also has data- select inputs, which permit digital data on any one of the inputs to be switched to the output line.

10 MUX-continued... A modern stereo system may have a switch that selects music from one of four sources: a cassette tape, CD, a radio tuner, or an auxiliary input such as audio from a VCR or DVD. The switch selects one of the electronic signals from one of these four sources and sends it to the power amplifier and speakers. In simple terms, this is what a multiplexer (MUX) does; it selects one of several input signals and passes it on to the output.

11 Functional diagram of MUX

12 Two-input multiplexer

13 Logic symbol for a 1-of-4 data selector/multiplexer.

14 LOGIC FUNCTION GENERATION USING MUX-Example 2 Implement the Boolean function F=x’y’z +x’yz’ + xyz’ + xyz using a suitable MUX

15 DEMULTIPLEXERS A DEMULTIPLEXER (DEMUX) basically reverses the multiplexing function. It takes data from one line and distributes them to a given number of output lines. For this reason, the demultiplexers is also known as a data distributor. A multiplexer takes several inputs and transmits one of them to the output. A demultiplexer (DEMUX) performs the reverse operation ; it takes a single input and distributes it over several outputs.

16 General demultiplexer Functional diagram:- The large arrow indicates one or more lines. The select i/p code determines to which output the DATA input will be transmitted In other words, the demultiplexer takes one data input source and selectively distributes it to 1 of N output channels just like multiposition switch.

17 A 1-line-to-4-line demultiplexer.

8085 architecture