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4221 BCD to 7-Segment decoder Answered

I'm looking for a 4221 BCD (not 8421) to 7-seg decoder IC. To be honest, I just want to copy the logic diagram to work on an assignment for my VHDL class. I can't find any ICs like this on google! Do they not exist? For what reason? Thanks, Daniel



10 years ago

The simplest way to get such a chip is to burn the truth table into an eprom. A0-A3 will be your 4221 BCD input and D0-D6 will be your 7-segment output. But your homework is to compile the table into VHDL, I guess.


10 years ago

I don't think there was ever such a thing made. Is 4221 supposed to have some cute advantages over other encoding schemes? (never heard of it as an encoding scheme, either.) Looks like digits other than 0 and 1 are going to have two possible representations, which I don't like much!


10 years ago

Do they not exist? For what reason?

I don't get your question...if you're searching, surely you know what they are (were) used for...( even the 6502 had a BCD mode.)

Or perhaps I misunderstand (like, are you interested in just one specific exotic IC?)

As far as discrete BCD to 7 segments (whipping out my Master IC Cookbook),

CMOS: 4511

TTL: 7446, 7448 (surely available in HC, etc versions)

From my assignment: "In your previous lab, you designed a BCD to 4221 encoder. In this lab, design a 4221 to 7-segment encoder." As in, an encoder from 4 inputs (switches) to 7 outputs (7-seg LED display). So 4221 (NOT 8421) to 7-segment. I am wholly capable of going through and doing all the K-maps, finding the s-o-p, minimizing it, and drawing the logic circuit, but I'd rather not as I'm extremely sick of them. I know there's gotta be a chip that already does this, with a nice schematic in the datasheet.

With a simple google search, I easily found datasheets for the 4511 and the 7448....with logic schematics. Beats me what a 4221 is...but if it's a BCD to 7 Segment, those diagrams should help...

4221 is a differently weighted BCD. e.g. the nibble "1001" would equal the decimal 5, and "0101" would equal 3. "0011" would also equal 3 by this system. It seems that all the IC's (at least, that I can find) are standard 8421 BCD only.

make your own diode matrix rom funsicle, like a popsicle with fun attached

Gotcha. I expect they knew it wasn't a "gimmie" when they set the curriculum.... Good luck.

or you could look for an overly complicated way to do it, oh say my instrucable about drivinga 7 segment display, but I don't know if that would apply to this.