PIC18F2221 MICROCHIP [Microchip Technology], PIC18F2221 Datasheet - Page 237

• Manufacturer Part Number: PIC18F2221
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

19.6
Figure 19-4 shows the operation of the A/D converter
after the GO/DONE bit has been set and the
ACQT2:ACQT0 bits are cleared. A conversion is
started after the following instruction to allow entry into
Sleep mode before the conversion begins.
Figure 19-5 shows the operation of the A/D converter
after the GO/DONE bit has been set and the
ACQT2:ACQT0 bits are set to ‘010’ and selecting a
4 T
Clearing the GO/DONE bit during a conversion will abort
the current conversion. The A/D Result register pair will
NOT be updated with the partially completed A/D
conversion sample. This means the ADRESH:ADRESL
registers will continue to contain the value of the last
completed conversion (or the last value written to the
ADRESH:ADRESL registers).
FIGURE 19-4:
FIGURE 19-5:
© 2007 Microchip Technology Inc.
(Holding capacitor continues
acquiring input)
Set GO/DONE bit
AD
1
acquisition time before the conversion starts.
T
CY
Set GO/DONE bit
T
A/D Conversions
Holding capacitor is disconnected from analog input (typically 100 ns)
ACQT
Acquisition
Automatic
- T
2
Time
AD
Conversion starts
Cycles
T
AD
3
1 T
A/D CONVERSION T
A/D CONVERSION T
AD
b9
4
2 T
Conversion starts
(Holding capacitor is disconnected)
AD
b8
1
3 T
AD
b9
2
b7
4 T
On the following cycle:
ADRESH:ADRESL is loaded, GO/DONE bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input.
AD
b8
3
b6
AD
AD
5 T
On the following cycle:
ADRESH:ADRESL is loaded, GO/DONE bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input.
CYCLES (ACQT<2:0> = 000, T
CYCLES (ACQT<2:0> = 010, T
Preliminary
AD
b7
b5
4
6 T
T
AD
b4
5
b6
AD
7 T
Cycles
After the A/D conversion is completed or aborted, a
2 T
started. After this wait, acquisition on the selected
channel is automatically started.
19.7
The discharge phase is used to initialize the value of
the capacitor array. The array is discharged before
every sample. This feature helps to optimize the unity-
gain amplifier, as the circuit always needs to charge the
capacitor array, rather than charge/discharge based on
previous measure values.
PIC18F4321 FAMILY
AD
b3
b5
Note:
6
AD
8
wait is required before the next acquisition can be
T
AD
b4
Discharge
b2
7
9 T
The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
AD
b3
8
b1
10
T
AD
b0
b2
ACQ
ACQ
9
11
= 0)
T
= 4 T
AD
10
Discharge
b1
1
AD
b0
11
DS39689E-page 235
)
T
Discharge
AD
1