> I have a circuit for which I am doing some reverse engineering. > > There is a wire link to the LCD keypad. the keypad has 12 buttons on it. > namely 1,2,3,4,5,6,7,8,9,0,#,* > the wire has 7 wires one for power and apparently the rest of the 6 wires > represent the 12 keys.
It sounds like 2-of-X encoding. Same style used on Touch Tone Phones. A Matrixs keyboard would not have a power wire to it, unless it is for some type of ESD protection, which is not likely. In 2-of-X assuming the power wire goes to ground, then there would be pull ups on the remaining lines. When you press a key, two of the lines will be pulled to the power rail to encode the key. If you have the memory space you use a 256 byte table to translate to some more useful code. 2-of-X has many advantages over X-Y scanning. 1) The key board is full static, add a three or four diodes and it can act as the power switch or wake up as well. 2) One static read gets it done, no complicated Matrix scanning code. 3) #2 also implies that your product will have a lot lower EMI since the key pad has no active drive signals going to it The one down side is that it takes a whole input port that you can't share with any thing. With X-Y you can share the drive lines with LEDs. > I wanted to know is there any standard combination for the keys. I cannot > apply power to check it out as I have to be careful not to blow the > circuit. > > Can anyone help? How can I check? Low current Ohm meeter? Grayhill makes the most commonly found 2-of-X keypads out side of those found in phones. See if yours matches one of theirs. -- Author: Bob Paddock INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
