Apparatus and method for scanning a key matrix
US5805085A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 26, 1996 |
| Grant date | Sep 8, 1998 |
| Priority date | — |
| Expiry date | Jul 26, 2016 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03M11/20
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
An apparatus and method for scanning a triangular or trapezoidal key matrix for data input by depressing keys of a keypad. The key matrix allows an increased number of keyswitches to be provided on the key matrix while reducing the number of I/O ports on the I/O interface. The apparatus includes an I/O interface connecting the keypad to the CPU. The keypad I/O interface is provided with m I/O ports, where m is plural integer. Through detecting the voltage levels of these I/O ports, the CPU is able to determine which key on the keypad is being depressed. A triangular key matrix is constructed with a set of m code lines and at least one auxiliary code line arranged in such a way as to form a triangular array of m.times.(m+1)/2 cross-points. Each cross-point is provided with a keyswitch associated with a key on the keypad. The m code lines are connected correspondingly to the m I/O ports on the keypad I/O interface. In another embodiment, a trapezoidal key matrix is constructed with m code lines and two auxiliary code line including a ground line and a power line arranged in such a way as to form an m-by-(m+1) trapezoidal array of m.times.(m+3)/2 cross-points. The method according to …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.