參數(shù)資料
型號: 16F872
廠商: Microchip Technology Inc.
英文描述: CAT 5E CROSSOVER PATCH CORD CABLE GREEN 10 FT
中文描述: 28引腳,8位閃存微控制器的CMOS
文件頁數(shù): 90/160頁
文件大?。?/td> 2600K
代理商: 16F872
PIC16F872
DS30221A-page 90
Preliminary
1999 Microchip Technology Inc.
10.2
Selecting the A/D Conversion Clock
The A/D conversion time per bit is defined as T
AD
. The
A/D conversion requires a minimum 12T
AD
per 10-bit
conversion. The source of the A/D conversion clock is
software selected. The four possible options for T
AD
are:
2T
OSC
8T
OSC
32T
OSC
Internal RC oscillator
For correct A/D conversions, the A/D conversion clock
(T
AD
) must be selected to ensure a minimum T
AD
time
of 1.6
μ
s.
Table 10-1shows the resultant T
AD
times derived from
the device operating frequencies and the A/D clock
source selected.
TABLE 10-1:
T
AD
vs. MAXIMUM DEVICE OPERATING FREQUENCIES (STANDARD DEVICES (C))
10.3
Configuring Analog Port Pins
The ADCON1, and TRIS registers control the operation
of the A/D port pins. The port pins that are desired as
analog inputs must have their corresponding TRIS bits
set (input). If the TRIS bit is cleared (output), the digital
output level (V
OH
or V
OL
) will be converted.
The A/D operation is independent of the state of the
CHS<2:0> bits and the TRIS bits.
AD Clock Source (T
AD
)
Maximum Device Frequency
Operation
ADCS<1:0>
Max.
2T
OSC
8T
OSC
32T
OSC
RC
(1, 2, 3)
00
1.25 MHz
5 MHz
20 MHz
Note 1
01
10
11
Note 1:
The RC source has a typical T
AD
time of 4
μ
s but can vary between 2-6
μ
s.
2:
When the device frequencies are greater than 1 MHz, the RC A/D conversion clock source is only recommended for sleep
operation.
3:
For extended voltage devices (LC), please refer to the Electrical Specifications section.
Note 1:
When reading the port register, any pin
configured as an analog input channel will
read as cleared (a low level). Pins config-
ured as digital inputs will convert an ana-
log input. Analog levels on a digitally
configured input will not affect the conver-
sion accuracy.
2:
Analog levels on any pin that is defined as
a digital input (including the AN<4:0>
pins), may cause the input buffer to con-
sume current that is out of the device
specifications.
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