PIC18F2480 MICROCHIP [Microchip Technology], PIC18F2480 Datasheet - Page 255

• Manufacturer Part Number: PIC18F2480
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

19.2
The ADCON2 register allows the user to select an
acquisition time that occurs each time the GO/DONE
bit is set.
When the GO/DONE bit is set, sampling is stopped and
a conversion begins. The user is responsible for ensur-
ing the required acquisition time has passed between
selecting the desired input channel and setting the
GO/DONE bit. This occurs when the ACQT2:ACQT0
bits (ADCON2<5:3>) remain in their Reset state (‘000’)
and is compatible with devices that do not offer
programmable acquisition times.
If desired, the ACQT bits can be set to select a
programmable acquisition time for the A/D module.
When the GO/DONE bit is set, the A/D module
continues to sample the input for the selected
acquisition
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.
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:
 2004 Microchip Technology Inc.
Note 1:
2:
3:
4:
Selecting and Configuring
Automatic Acquisition Time
Operation
The RC source has a typical T
The RC source has a typical T
For device frequencies above 1 MHz, the device must be in Sleep for the entire conversion or the A/D
accuracy may be out of specification.
Low-power (PIC18LFXXXX) devices only.
16 T
32 T
64 T
2 T
4 T
8 T
time,
RC
OSC
OSC
OSC
OSC
OSC
OSC
(3)
AD Clock Source (T
T
AD
then
vs. DEVICE OPERATING FREQUENCIES
automatically
ADCS2:ADCS0
AD
)
AD
AD
000
100
001
101
010
110
x11
begins
time of 4 ms.
time of 6 ms.
PIC18F2480/2580/4480/4580
Preliminary
a
19.3
The A/D conversion time per bit is defined as T
A/D conversion requires 11 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 T
for more information).
Table 19-1 shows the resultant T
the device operating frequencies and the A/D clock
source selected.
PIC18F2X80/4X80
AD
) must be as short as possible, but greater than the
1.00 MHz
1.25 MHz
2.50 MHz
5.00 MHz
10.0 MHz
20.0 MHz
40.0 MHz
OSC
OSC
OSC
OSC
OSC
OSC
Selecting the A/D Conversion
Clock
Maximum Device Frequency
AD
(approximately 2 s, see parameter 130
(1)
PIC18LF2X80/4X80
AD
per 10-bit conversion.
AD
1.00 MHz
10.65 MHz
21.33 MHz
1.33 MHz
2.66 MHz
5.33 MHz
DS39637A-page 253
666 kHz
times derived from
(2)
AD
(4)
. The
AD
: