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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： | 擴展數(shù)字輸入與A / D轉(zhuǎn)換器 |
| 文件頁數(shù)： | 3/12頁 |
| 文件大?。?/td> | 283K |
| 代理商： | AN1775 |
Application Note
Implementation
AN1775 Rev. 1
ADC Alternative
In many cases, input pins are at a premium. One can't always freely
assign input pins to the function of user input. A more efficient use of
microcontrollerresourcescanbedevised.Onecommonfeatureofmany
Freescale MCUs is the analog-to-digital converter, or ADC.
The ADC of a Freesca;e MCU usually features four to eight channels of
analog input, which is compared with a reference voltage and converted
to an 8-bit digital value. When a resistor ladder is connected to an analog
input through switches in each segment, the conversion result can be
used to arbitrate an input. This allows many keys to be interfaced with
one input pin, with only a little more software overhead.
Figure 2
shows
such an implementation.
Figure 2. Resistor Ladder Keys Using an Analog Input Pin
Implementation
ADC Operation
An MCU ADC typically has 8-bit precision. This means there are 2
8
, or
256, distinguishable A/D inputs, including 0. The analog inputs are
converted to a binary number, which represents the magnitude of the
input voltage in relation to a reference voltage.
V
DD
ADC
INPUT
PIN
MCU
V
In
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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