PIC18F2331/2431/4331/4431
Clearing the GO/DONE bit during a conversion will
abort the current conversion. The resulting buffer loca-
tion will contain the partially completed A/D conversion
sample. This will not set the ADIF flag, therefore, the
user must read the buffer location before a conversion
sequence overwrites it.
21.9 A/D Conversions
Figure 21-3 shows the operation of the A/D Converter
after the GO/DONE bit has been set and the
ACQT<2:0> bits are cleared. A conversion is started
after the following instruction to allow entry into Sleep
mode before the conversion begins. The internal A/D
RC oscillator must be selected to perform a conversion
in Sleep.
After the A/D conversion is completed or aborted, a
2 TAD wait is required before the next acquisition can be
started. After this wait, acquisition on the selected
channel is automatically started.
Figure 21-4 shows the operation of the A/D Converter
after the GO/DONE bit has been set, the ACQT<3:0>
bits are set to ‘010’ and a 4 TAD acquisition time is
selected before the conversion starts.
Note: The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
FIGURE 21-3:
GO/DONE bit is
A/D CONVERSION TAD CYCLES (ACQT<2:0> = 000, TACQ = 0)
TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b6
set and holding
cap is
b8
b4
b3
b2
b9
b5
b7
b0
b1
disconnected
from analog
input
Conversion Starts
GO/DONE bit cleared on the rising edge of Q1 after the first Q3
following TAD11 and result buffer is loaded.(1)
Note 1: Conversion time is a minimum of 11 TAD + 2 TCY and a maximum of 11 TAD + 6 TCY.
FIGURE 21-4:
A/D CONVERSION TAD CYCLES (ACQT<3:0> = 0010, TACQ = 4 TAD)
TACQT Cycles
TAD Cycles
1
2
3
4
TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b6
b9
Conversion Starts
(Holding capacitor is disconnected)
b8
b5
b4
b3
b2
b7
b0
b1
Automatic
Acquisition
Time
A/D Triggered
GO/DONE bit cleared on the rising edge of Q1 after the first Q3
following TAD11 and result buffer is loaded.(1)
Note 1: In Continuous modes, next conversion starts at the end of TAD12.
2010 Microchip Technology Inc.
DS39616D-page 253
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