PIC18F2420 MICROCHIP [Microchip Technology], PIC18F2420 Datasheet - Page 233

• Manufacturer Part Number: PIC18F2420
• 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 bit has been set and the ACQT2:ACQT0
bits are cleared. A conversion is started after the follow-
ing 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 bit has been set and the ACQT2:ACQT0
bits are set to ‘010’ and selecting a 4 T
time before the conversion starts.
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:
 2004 Microchip Technology Inc.
(Holding capacitor continues
acquiring input)
Set GO bit
1
T
CY
Set GO 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
AD
4 T
acquisition
On the following cycle:
ADRESH:ADRESL is loaded, GO bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input.
AD
PIC18F2420/2520/4420/4520
b8
3
b6
AD
AD
5 T
On the following cycle:
ADRESH:ADRESL is loaded, GO bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input.
CYCLES (A
CYCLES (A
Preliminary
AD
b5
b7
4
6 T
T
AD
b4
5
b6
AD
7 T
Cycles
After the A/D conversion is completed or aborted, a
2 T
be 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.
CQT
AD
CQT
b3
b5
Note:
6
AD
8
<2:0> = 000, T
<2:0> = 010, T
wait is required before the next acquisition can
T
AD
b4
b2
Discharge
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
ACQ
b0
b2
9
ACQ
11
T
= 0)
AD
10
= 4 T
Discharge
b1
1
AD
b0
DS39631A-page 231
11
)
T
Discharge
AD
1