PIC18F8493 Microchip Technology, PIC18F8493 Datasheet - Page 39

• Manufacturer Part Number: PIC18F8493
• Description: Flash Microcontrollers
• Manufacturer: Microchip Technology

2.6
Figure 2-4 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 2-5 shows the operation of the A/D Converter
after
ACQT2:ACQT0 bits are set to ‘010’ and a 4 T
sition time has been selected 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 2-4:
FIGURE 2-5:
© 2009 Microchip Technology Inc.
(Holding capacitor continues
acquiring input)
Set GO/DONE bit
T
Set GO/DONE bit
CY
Holding capacitor is disconnected from analog input (typically 100 ns)
1
– T
the
T
ACQT
A/D Conversions
Acquisition
AD
Automatic
2
Time
T
GO/DONE
AD
Cycles
1 T
3
Conversion starts
b11
AD
A/D CONVERSION T
2 T
A/D CONVERSION T
4
bit
AD
b10
1
3 T
has
Conversion starts
(Holding capacitor is disconnected)
AD
b11
b9
2
4 T
been
b10
AD
On the following cycle:
ADRESH:ADRESL are loaded, GO/DONE bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input
3
b8
5 T
On the following cycle:
ADRESH:ADRESL are loaded, GO/DONE bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input
set,
AD
PIC18F6393/6493/8393/8493
AD
AD
b9
AD
4
b7
acqui-
6 T
CYCLES (ACQT<2:0> = 000, T
CYCLES (ACQT<2:0> = 010, T
the
b8
5
AD
b6
7 T
b7
T
6
AD
AD
b5
8
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.
2.7
The discharge phase is used to initialize the value of
the holding capacitor. 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.
b6
7
Note:
T
AD
AD
b4
wait is required before the next acquisition can
9 T
b5
8
Discharge
AD
b3
The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
Code should wait at least 2 μs after
enabling the A/D before beginning an
acquisition and conversion cycle.
10
b4
9
T
AD
b2
11
10
b3
ACQ
T
ACQ
AD
b1
11
b2
12
= 0)
= 4 T
T
AD
b0
12
b1
13
AD
)
T
DS39896B-page 39
Discharge
(typically 200 ns)
www.DataSheet4U.com
b0
13
AD
1
T
Discharge
(typically
200 ns)
AD
1