7447 IC - eclubiitk/EClub-Handbook GitHub Wiki

74LS47 is a BCD to 7-segment decoder/driver IC. It accepts a binary coded decimal as input and converts it into a pattern to drive a seven-segment for displaying digits 0 to 9. 0000=0, 0001=1,0010=2,……,1001=9. Binary coded decimal (BCD) is an encoding in which each digit of a number is represented by its own binary sequence (usually of four bits).

Description

74LS47 IC accepts four lines of BCD (8421) input data at pins A,B,C and D and generates their complements internally. The data is decoded with seven AND/OR gates to drive indicator LEDs of the seven segment directly. Display patterns for BCD input counts above nine are unique symbols to authenticate input conditions.

LT' stands for Lamp Test. When LT' is low all the segments on the 7-seg display are lit regardless of A,B,C,D.

BI' stands for Blanking Input. When BI' is low the display is blank so all the segments on the 7 seg display are off regardless of A,B,C,D

RBI' stands for Ripple Blanking Input. When RBI' is low and DCBA=0000 the display is blank otherwise the number is displayed on the display. This is used to remove leading zeroes from a number (e.g. display 89 instead of 089). To use with more than one display, connect RBO'(Ripple Blanking Output) from most significant 74xx47 to the RBI' of the next 74xx47.

Connect RBI' of the least significant 74xx47 to 5v unless you want the diplay to turn off when the number is 0.

The following picture clarifies the functioning a bit

Here the boxes represent 1 * 1 + 1 * 2 + 0 * 4 + 0 * 8 = 3 which is shown in the LED display.

The datasheet is available here