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參數(shù)資料
| 型號： | AN1775 |
| 廠商： | 飛思卡爾半導(dǎo)體(中國)有限公司 |
| 英文描述： | Expanding Digital Input with an A/D Converter |
| 中文描述： | 擴(kuò)展數(shù)字輸入與A / D轉(zhuǎn)換器 |
| 文件頁數(shù)： | 2/12頁 |
| 文件大?。?/td> | 283K |
| 代理商： | AN1775 |
Application Note
AN1775 Rev. 1
Background
Dedicated Input
A microcontroller typically receives user input through digital input pins.
The simplest implementation is a single switch directly connected to a
digital input pin. This is easy to realize, but is not the most efficient use
of resources, with one pin dedicated to one input. One port data bit
represents the state of one switch.
Matrix Input
Another method uses a keypad, a common element in embedded
systems. These are ordinarily arranged in a matrix, as shown in
Figure 1
. In this case, the byte value of an entire port data register can
be polled to determine which key was pressed. This is more efficient, as
a 4 x 4 keypad can interface 16 keys with eight input pins.
Figure 1. Resistor Matrix Keypad Using Parallel Port Pins
P x 0
P x 1
P x 2
P x 3
P x 4
P x 5
P x 6
P x 7
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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