PIC18F2423 MICROCHIP [Microchip Technology], PIC18F2423 Datasheet - Page 235

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PIC18F2423

Manufacturer Part Number
PIC18F2423
Description
28/40/44-Pin, Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt Technology
Manufacturer
MICROCHIP [Microchip Technology]
Datasheet

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19.2
The ADCON2 register allows the user to select an
acquisition time that occurs each time the GO/DONE
bit is set. It also gives users the option to use an
automatically determined acquisition time.
Acquisition time may be set with the ACQT2:ACQT0
bits (ADCON2<5:3>), which provides a range of 2 to
20 T
continues to sample the input for the selected acquisi-
tion time, then automatically begins a conversion.
Since the acquisition time is programmed, there may
be no need to wait for an acquisition time between
selecting a channel and setting the GO/DONE bit.
Manual
ACQT2:ACQT0 = 000. When the GO/DONE bit is set,
sampling is stopped and a conversion begins. The user
is responsible for ensuring the required acquisition time
has passed between selecting the desired input
channel and setting the GO/DONE bit. This option is
also the default Reset state of the ACQT2:ACQT0 bits
and is compatible with devices that do not offer
programmable acquisition times.
In either case, when the conversion is completed, the
GO/DONE bit is cleared, the ADIF flag is set and the
A/D begins sampling the currently selected channel
again. If an acquisition time is programmed, there is
nothing to indicate if the acquisition time has ended or
if the conversion has begun.
TABLE 19-1:
© 2007 Microchip Technology Inc.
Note 1:
AD
. When the GO/DONE bit is set, the A/D module
2:
Selecting and Configuring
Acquisition Time
The RC source has a typical T
For device frequencies above 1 MHz, the device must be in Sleep for the entire conversion or a F
divider should be used instead. Otherwise, the A/D accuracy specification may not be met.
acquisition
Operation
16 T
32 T
64 T
2 T
4 T
8 T
T
RC
AD
OSC
OSC
OSC
OSC
OSC
OSC
(2)
vs. DEVICE OPERATING FREQUENCIES
A/D Clock Source (T
is
selected
AD
time of 2.5 μs.
PIC18F2423/2523/4423/4523
AD
when
)
Preliminary
ADCS2:ADCS0
000
100
001
101
010
110
x11
19.3
The A/D conversion time per bit is defined as T
A/D conversion requires 13 T
The source of the A/D conversion clock is software
selectable. There are seven possible options for T
• 2 T
• 4 T
• 8 T
• 16 T
• 32 T
• 64 T
• Internal RC Oscillator
For correct A/D conversions, the A/D conversion clock
(T
minimum
information).
Table 19-1 shows the resultant T
the device operating frequencies and the A/D clock
source selected.
AD
) must be as short as possible, but greater than the
OSC
OSC
OSC
OSC
OSC
OSC
Selecting the A/D Conversion
Clock
T
AD
(see
Assumes T
parameter
Maximum F
1.00 MHz
10.00 MHz
20.00 MHz
40.00 MHz
40.00 MHz
AD
2.50 MHz
5.00 MHz
AD
per 12-bit conversion.
AD
Min. = 0.8 μs
DS39755B-page 233
times derived from
130
(1)
OSC
for
OSC
AD
. The
more
AD
:

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