4X4 matrix keypad-74c922- source code

hi...... im trying to interface a 4x4 matrix keypad using a 74c922 decoder to an Atmel micrcontroller ...in c- programm.......

i would appreciate some pointers in how to create d source code that will read from the output of the decoder...according to key pressed...

thxs bb

Reply to
bb
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Hi, bb. Assuming you're using external caps for the oscillator and the keybounce mask, all you have to do is set your keycheck loop so it happens at least twice during the component-selected debounce period.

Check for Data Available. If it's high, read the keypress data, then set a software flag. Don't read data while the flag is set. Wait for Data Available to be low again before resetting the flag. Read data again when flag is reset and Data Available is high.

If you don't need to tri-state the '922 data outputs, that's the easiest way. If you have bussed the data, clear the bus and then toggle output enable to read the data as above. It's all in the data sheet, available at the Fairchild Semiconductor website.

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If this isn't an exercise in programming, though, the 74C922 is an expensive way to do this job. If your code is so bound up that you need a dedicated part to do keypad debounce, it might be better to get another small uC to do this job at less cost and fewer pins (data can also be sent from one uC to the other in serial format). You can also have n-key rollover instead of just 2-key quite easily.

There's no law that says you can't have more than one uC on a board.

Good luck Chris

Reply to
Chris

thx chris....

adding uc was an option i thought about earlier but d cct handles lots more function than just keypad reading...tis includes alarm,lcd interface,relays n stuff...n i hv only 6 IO lines to spare.... besides... the cct is already made finalize

wht i still dont get is tis

a) how to make a source code that will enable uc read d 5 input taken from

74c922....74c922 takes in 16 values(from 4x4 matrix) and decode it into a 4 bit binary code to the uc plus a DA line..... do i hv to include d conversion table(from 16 to 5) in the program source code?

b)how do i know whts d approprite delay time for key bounce routine....if im using an atmel89s8252..is there a mathematical calculation involved in estimating it?

c)and finally in c -language.... is library file-> reg52.h, reg51.h and declaration term'sbit'....ANSI standard...?

when i compile d program it gives me error..cannot define reg 52.h and term sbit im using turbo c++ 4.5

:-)

Reply to
bb

Hi, bb. In the data sheet, it shows how to calculate the debounce time based on the caps selected. Read the data sheet.

You should be able to read the DA bit directly in C. Just jump on zero or not zero. As far as the 4-bit pushbutton data, you can read the byte, mask off the bits you don't need, rearrange if necessary (usually the case -- somehow, it seems to be trivially easy to transpose bits on a PC board), then shift as necessary to make it the low nybble. Then just read the data. Or if it takes fewer instructions/time, read the four bits individually, then multiply/shift as necessary and add to form the data nybble. Your call.

I don't know the Atmel C compiler you're talking about. If you need help with code, you might want to go to one of the Atmel groups.

I've found it usually helps a lot to read the manuals and data sheets. Even if you spend some time looking, that's just a free opportunity to learn something else along the way.

By the way, please take a chance to glance at this:

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and also, please don't use TXT lingo unless you're posting from your cell phone. Us older cripples find it somewhat obscure. I know -- our problem, and we'll soon enough be dead. But if fossils can't understand, fossils can't help, can they?

And it actually sounds more like the TXT lingo poster can't even take the time or show the respect to express himself carefully. Whether that's interpreted as panic, extreme hurry, or a lack of respect by the person who's taking the time to help and craft a response, it probably won't help the OP.

And a fossil might just answer:

havnt a clue wot U' spoutin', m8. hOp U git out of d car trunk s%n!

(

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for us fossils out there ;-)

Good luck Chris

Reply to
Chris

hehe....

thank you chris.....understanding the needs of fossil over here( can you see...all lengthy words-ohmygoditiskilling-but its ok )...

young blokes lik me always in a hurry.....*wink *wink *smile

Reply to
bb

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