Getting 16 outputs from only 6 Pins - CD74HC4514

[bitfogav]

Hi everyone I just wanted to point out this CMOS Logic 4 to 16 line chip that I have been studying and working with.

It is a CD74HC4514 by texas intruments, it uses only 6 I/O lines from your microchip and gives you 16 I/O lines as a decoder, it is also a demultiplexer.

Might be handy for a 8 x 8 or 16 x 16 display of some kind

[brad]

I was actually looking into the same chip when thinking of a new project a while ago. The problem was that they seemed to be hard to come by.

Have you managed to find any?

[bitfogav]

well my supply so far has been Ebay but you can also get them from Farnell

[brad]

The only problem I have found with searching for parts on ebay is that there are loads of variations for the same chip.

E.G. if I wanted a 74373 i would do a search for a 74373, but people may be listing them as 74l373, 74hc373 74as373 74hct373 74als373 or even many other variations of these. I think it would be great if ebay included wildcards in their search feature.

[bitfogav]

Yeah I guess your right people do list all sorts of variations for this chip and a few others, but if you make sure what they are selling is what you want then should be ok, but if your not sure then you can always ask the seller for more details?

I have used the 74HC4514 and 74HCT4514 variations of this chip, I would recommend using the 74HCT4514 variation as this chip uses TTL inputs so works directly connected to your microchip, but if you find yourself with a 74HC4514 then this uses CMOS inputs, which makes it slightly more difficult when connecting it to a microchip.

For an example a CMOS Input to be a logic 1 state as to be at votage levels 3.5v or above, where as a TTL logic 1 state as to be at 2v or above to be a logic 1. ( check out the picture below )

So I have found to over come this issue we use a pull-up resistor connected on the data lines, this then helps to give us our 3.5v voltage levels. (Ive used a 1K pull-up resistor)

[brad]

ah yes, sorry - what I meant was that sometimes it is hard to find or takes a long time to find a certain part because there are so many variations. You need to type in just about every part number including the electrical characteristics and there could be loads of different variations.

As for the CMOS / TTL levels - I just taught that in one of my digital classes a couple of days ago, Actually, the students have their exam today, let's see if they get that stuff correct

[bitfogav]

ahh yeah sorry I see what you mean now

Most of the stuff ive learnt has just been self taught, I bet your classes are really good, looking at all your projects and how you present them..
would like to attend some of your classes hehe!, I bet I would learn alot!!

[brad]

Self taught is just about the best way to do it!

Actually, Google is probably the best way to learn just about anything!

That's where I started in programming