PIC18FXX39 Datasheet, PDF (187/322 Pages) Microchip Technology – Enhanced FLASH Microcontrollers with Single Phase Induction Motor Control Kernel

PIC18FXX39
18.4 A/D Conversions
Figure 18-3 shows the operation of the A/D converter
after the GO bit has been set. Clearing the GO/DONE
bit during a conversion will abort the current conver-
sion. The A/D result register pair will NOT be updated
with the partially completed A/D conversion sample.
That is, the ADRESH:ADRESL registers will continue
to contain the value of the last completed conversion
(or the last value written to the ADRESH:ADRESL reg-
isters). After the A/D conversion is aborted, a 2 TAD wait
is required before the next acquisition is started. After
this 2 TAD wait, acquisition on the selected channel is
automatically started. The GO/DONE bit can then be
set to start the conversion.
Note: The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
FIGURE 18-3:
A/D CONVERSION TAD CYCLES
TCY - TAD TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b9 b8 ^{b7 b6 b5 b4 b3 b2 b1 b0 b0}
Conversion Starts
Holding capacitor is disconnected from analog input (typically 100 ns)
Set GO bit
Next Q4: ADRESH/ADRESL is loaded, GO bit is cleared,
ADIF bit is set, holding capacitor is connected to analog input.
18.4.1 A/D RESULT REGISTERS
The ADRESH:ADRESL register pair is the location
where the 10-bit A/D result is loaded at the completion
of the A/D conversion. This register pair is 16-bits wide.
The A/D module gives the flexibility to left or right justify
the 10-bit result in the 16-bit result register. The A/D
FIGURE 18-4:
A/D RESULT JUSTIFICATION
Format Select bit (ADFM) controls this justification.
Figure 18-4 shows the operation of the A/D result justi-
fication. The extra bits are loaded with ‘0’s. When an
A/D result will not overwrite these locations (A/D
disable), these registers may be used as two general
purpose 8-bit registers.
10-bit Result
ADFM = 1
ADFM = 0
7
2107
0
0000 00
ADRESH
ADRESL
10-bit Result
Right Justified
7
0765
0
0000 00
ADRESH
ADRESL
10-bit Result
Left Justified
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Preliminary
DS30485B-page 187