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參數(shù)資料
| 型號(hào)： | AN1775 |
| 廠商： | 飛思卡爾半導(dǎo)體(中國(guó))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)： | 6/12頁 |
| 文件大?。?/td> | 283K |
| 代理商： | AN1775 |
Application Note
AN1775 Rev. 1
Some notes on the spreadsheet:
V
In
is determined by decrementing the high voltage reference by
the voltage step for each segment in the ladder. (See
Figure 4
.)
Rn is the resistor value of the current key segment needed to form
desired equivalent resistance Req.
Req represents the equivalent resistance of ladder, including the
current resistor (Rn) and excluding the pullup resistor (R0).
Vinmin and Vinmax are the minimum and maximum voltages that
can be arbitrated as a particular key. In this case, V
In
+/–Vstep/2
was used.
ADDRmin and ADDRmax are the ADC data register value range
used to represent a given keypress. This range can be narrowed
or widened to affect precision. In this case, the ranges were
maximized, so no conversion result is undefined.
This particular spreadsheet did not use resistor precision, but this
could be considered to further pad the error.
Table 1. Spreadsheet Calculations
V
DD
=
# Keys =
Voltage Steps =
5
8
0.625 (V
DD
/# Keys)
Converter Resolution =
0.01961
(Vdd/255)
R0 =
10000
(Pullup)
(Hex)
ADDRmin
EF
0
F
2F
4F
6F
8F
AF
CF
(Hex)
ADDRmax
FF
F
2F
4F
6F
8F
AF
CF
EF
Key pressed
No Key
1
2
3
4
5
6
7
8
V
In
5
0
0.625 1429
1.25
1.875 6000
2.5
3.125 16667
3.75
4.375 70000
Req
0
0
Rn
10000
0
1429
1904
2667
4000
6667
13333
40000
Vinmin
4.6875
0
0.3125
0.9375
1.5625
2.1875
2.8125
3.4375
4.0625
Vinmax
5
0.3125
0.9375
1.5625
2.1875
2.8125
3.4375
4.0625
4.6875
3333
10000
30000
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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