Using a CPLD to Implement a QWERTY Keypad
As cell phones and other portable handheld devices continue to add features, design trade-offs are constantly evolving. Popular features such as text messaging and web browsing demand more data entry, but that can be cumbersome with traditional dual tone multiple frequency (DTMF) (0-9, #, *) keypads. Using this type of keypad requires multi-tap data entry, which is inefficient and error-prone.
One option to make text entry easier is to use a QWERTY keypad. This type of keypad employs 40 or more keys versus the normal 12 in a DTMF handset, although the additional keys make the handset larger and involve more electronic components.
Text message users may be willing to trade size for a QWERTY keypad; text entry is much easier and you can use two thumbs to enter text messages or data. Recently, some cell phone manufacturers have released handsets with QWERTY keypads that cater to text users.
There are many ways to design data entry keypads, but no standard exists. In this article, we’ll examine one possible solution to the design challenge of adding additional keys to a traditional DTMF-type keypad.
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