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PIC16F87XATI/SP Datasheet - Page 131

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11.2
Selecting the A/D Conversion
Clock
The A/D conversion time per bit is defined as T
A/D conversion requires a minimum 12 T
conversion. The source of the A/D conversion clock is
software selected. The seven possible options for T
are:
• 2 T
OSC
• 4 T
OSC
• 8 T
OSC
• 16 T
OSC
• 32 T
OSC
• 64 T
OSC
• Internal A/D module RC oscillator (2-6 s)
For correct A/D conversions, the A/D conversion clock
(T
) must be selected to ensure a minimum T
AD
of 1.6 s.
Table 11-1 shows the resultant T
times derived from
AD
the device operating frequencies and the A/D clock
source selected.
TABLE 11-1:
T
vs. MAXIMUM DEVICE OPERATING FREQUENCIES (STANDARD DEVICES (F))
AD
AD Clock Source (T
Operation
2 T
OSC
4 T
OSC
8 T
OSC
16 T
OSC
32 T
OSC
64 T
OSC
(1, 2, 3)
RC
Note 1:
The RC source has a typical T
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 (LF), please refer to Section 17.0 “Electrical Characteristics”.
 2001-2013 Microchip Technology Inc.
11.3
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
. The
AD
analog inputs must have their corresponding TRIS bits
per 10-bit
AD
set (input). If the TRIS bit is cleared (output), the digital
output level (V
OH
AD
The A/D operation is independent of the state of the
CHS2:CHS0 bits and the TRIS bits.
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 analog
input. Analog levels on a digitally config-
ured input will not affect the conversion
accuracy.
2: Analog levels on any pin that is defined as
time
AD
a digital input (including the AN7:AN0
pins) may cause the input buffer to con-
sume current that is out of the device
specifications.
)
AD
ADCS2:ADCS1:ADCS0
000
100
001
101
010
110
x11
time of 4 s but can vary between 2-6 s.
AD
PIC16F87XA
or V
) will be converted.
OL
Maximum Device Frequency
1.25 MHz
2.5 MHz
5 MHz
10 MHz
20 MHz
20 MHz
(Note 1)
DS39582C-page 131

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