PIC18F1230 MICROCHIP [Microchip Technology], PIC18F1230 Datasheet - Page 171

• Manufacturer Part Number: PIC18F1230
• Description: 18/20/28-Pin, Enhanced Flash Microcontrollers with nanoWatt Technology, High-Performance PWM and A/D
• Manufacturer: MICROCHIP [Microchip Technology]

© 2006 Microchip Technology Inc.
15.3
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 provide a range of 2 to 20 T
When the GO/DONE bit is set, the A/D module
continues to sample the input for the selected acquisition
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 15-1:
Note 1:
2:
3:
4:
Selecting and Configuring
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 (PIC18LF1230/1330) devices only.
16 T
32 T
64 T
acquisition
2 T
4 T
8 T
RC
OSC
OSC
OSC
OSC
OSC
OSC
(3)
AD Clock Source (T
T
AD
vs. DEVICE OPERATING FREQUENCIES
is
selected
ADCS2:ADCS0
AD
)
AD
AD
000
100
001
101
010
110
x11
Advance Information
time of 1.2 s.
time of 2.5 s.
when
AD
.
15.4
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
information).
Table 15-1 shows the resultant T
the device operating frequencies and the A/D clock
source selected.
PIC18F1230/1330
AD
11.43 MHz
22.86 MHz
) must be as short as possible, but greater than the
1.00 MHz
2.86 MHz
5.71 MHz
40.0 MHz
40.0 MHz
OSC
OSC
OSC
OSC
OSC
OSC
Selecting the A/D Conversion
Clock
PIC18F1230/1330
Maximum Device Frequency
T
AD
(1)
(see
parameter
PIC18LF1230/1330
AD
per 10-bit conversion.
AD
1.00 MHz
22.86 MHz
22.86 MHz
11.43 MHz
2.86 MHz
5.72 MHz
1.43 kHz
DS39758B-page 169
times derived from
130
(2)
for
AD
(4)
. The
more
AD
: