BCD to 7-segment decoder ....?

Question

Hi everyone,
I have a course in Digital systems, and it blows my mind when it comes to decoders, multiplixers and flipflops. Here is what it is; a decoder is an IC with an input of (n) and output of (2^n) like 2x4 decoder or 3x8 decoder. What I know is that the inputs determine which single output is; e.g, input (011)>> output is the signal in the third pin or lamp. HOWEVER, when it comes to BCD to 7 segment decoder:-
1- the output is not in the form of (2^n)
2- how can a decoder have an output of more than one pin (it is not an encoder, if you know what I mean).
3- the input are 4 pins, which means that 16 pins are supposed to be there.
4- If that was an encoder and not a decoder, then the input should be 2^7, right?


So guys help me as much as u can, thnx in advance!!!

Answer 1

Using the model of the Texas SN7447 BCD to 7 Segment decoder :



1. The output is in the form "a" through "g" where a.....g represent the seven segments of the display. Two or more segments may be illuminated at once depending on the input.



2. See the logic diagram on page 5 of the data sheet http://www.ti.com/lit/ds/symlink/sn7447a.pdf Think of it as a memory indexed array with predetermined outputs at 10 addresses like an EPROM so value X input will output data Y from address X where X is the BCD input "address" value and Y is the desired 7 segment output. Full truth tables are shown in the datasheet.



Decoder is perhaps a misnomer, perhaps "converter" would be a better description of its function and you could replace it with an eprom and some inverters on the output to manage the LED current. If you used an eprom you could expand the function to make it a hex display which would give you A,b,c,d,E,F in addition to 0-9. You'd differentiate 6 and b by illuminating the "a" segment for the number 6.



3. The 7447 is a 16 pin DIL package, the pin-out is on page 1 of the datasheet.



4. The input is BCD and it's a decoder. Even if it was an encoder it would not have a 2⁷ output per se, 7 bits yes but in a weird order that makes even Gray Encoding look sensible. Each BCD number input illuminates the relevant segments to display the number. It's not going to be mathematical as the displayed digits on a 7 segment display are symbolic representations of the numbers 0-9, you're drawing a picture.

Answer 2

Don't confuse yourself! I suggest that you visit your

local library and read up/on Digital Electronics. You

need to see schematics in order to understand how

these components work together. A BCD to 7 segment

decoder is used to drive a 7 segment LED package.

The input of this decoder is Binary Logic (0's & 1's).

I hope that your course includes some lab time. I have

studied electronics for many years and found that hands-

on experience is the best. You need to know how these

components connect in a given circuit/application to

get a better understanding. This should help you. If this

is a class in school; consult your instructor/professor.

He/she should be able to assist you in this matter.

Never be afraid to ask any professional anything for

their knowledge is power that will be gladly givin to you!

Feel free to e-me. Happy Holidays!

Answer 3

as pointed out look at the datasheets as an example these will allow you to look at the truth tables for the pinouts and explain how it functions, i the bcd to 7 seg is a bcd - hex converter so the output are in hex.