Dewan Tanvir Ahmed SITE, UofO Tutorial: ITI1100 Dewan Tanvir Ahmed SITE, UofO

General Decoder Diagram Decoders Decoder - logic circuit that activates an output that corresponds to a binary number on the input (set of inputs). General Decoder Diagram Demo

Decoder A n-to-m decoder a binary code of n bits = 2n distinct information n input variables; up to 2n output lines only one output can be active (high) at any time

Three-line-to 8-line (or 1-of-8) decoder

Decoder (cont..) Expansion two 3-to-8 decoder: a 4-to-16 deocder a 5-to-32 decoder?

Decoder (cont..) each output = a minterm use a decoder and an external OR gate to implement any Boolean function of n input variables A full-adder S(x,y,x)=S(1,2,4,7) C(x,y,z)= S(3,5,6,7)

Lab-3 Something like this:

BCD to 7-Segment Display Design Requirements Design the logic circuitry that will drive a seven segment LED display and will be able to represent numbers from 0 to 9 The BCD to 7-segment decoder performs a common function: it converts the binary representation of a decimal digit, 0000 to 1001, to the signals needed to show the digit on a 7 segment display.

Possible numbers and their representation on 7 segment display

Truth Table

Signal b implementation X1X0 00 01 11 10 X3X2 1  1  1  1    0  X     X X X  b = f(X3, X2, X1, X0) = X1’X0’ + X1X0 + X2’

Signal c implementation X1X0 00 01 11 10 X3X2 1  1  1   0  1   X     X X X  c = f(X3, X2, X1, X0) = X1’+ + X0 + X2

7 segment display All the anode segments are connected together Power must be applied externally to the anode connection that is common to all the segments By applying the ground to a particular segment (i.e. a,b,g etc..), the appropriate segment will light up

7 segment common anode A resistor should be added in order to limit the current through LED The current to light the active LED is sink by the logic component, which is preferable

7 segment display All the cathode of the LED are connected together The common connection must be grounded and power must be applied to appropriate segment in order to illuminate that segment The current to light the active LED is generated by the logic component, which generates the logic 1

BCD to 7 Segment Decoder/Drivers Common-anode : requires VCC , LED ON when Output is LOW. Common-cathode : NO VCC , LED ON when Output is HIGH. TTL and CMOS devices are normally not used to drive the common-cathode display directly because of current (mA) requirement. A buffer circuit is used between the decoder chips and common-cathode display

7447 TTL IC Real world example of BCD to 7 segment decoder Outputs of the decoder are active low and a common anode 7 segment display is used

Lab: BCD to 7 Segment Decoder/Drivers (a) BCD-to-7-segment decoder/driver driving a common-anode 7-segment LED display; (b) segment patterns for all possible input codes.

Multiplexers (Data Selectors) A multiplexer (MUX) selects one of multiple input signals and passes it to the output. The basic two input multiplexer The four input multiplexer The eight input multiplexer

Multiplexers (Data Selectors) A multiplexer (MUX) selects 1 out of N input data sources and transmits the selected data to a single output

Multiplexers Two-input multiplexer

Multiplexers Four-input multiplexer Four-input multiplexer - using sum of products logic

Multiplexers Eight-input multiplexer: The 74151

Multiplexers Eight-input multiplexer

Multiplexers (cont..)

Boolean function implementation MUX: a decoder + an OR gate 2n-to-1 MUX can implement any Boolean function of n input variable a better solution: implement any Boolean function of n+1 input variable n of these variables: the selection lines the remaining variable: the inputs

Multiplexers (cont..) Example: F(A,B,C)=S(1,3,5,6)

Multiplexers (cont..) Procedure: assign an ordering sequence of the input variable the leftmost variable (A) will be used for the input lines assign the remaining n-1 variables to the selection lines w.r.t. their corresponding sequence list all the minterms in two rows (A' and A) circle all the minterms of the function determine the input lines

Multiplexers (cont..) An example: F(A,B,C,D)=S(0,1,3,4,8,9,15)

Exercise Try to build an inverter using 2-1 MUX Try to build XOR gate using 4-1 MUX

Lab: Multiplexers Four-input multiplexer - using sum of products logic

Thank You!