PIC18F6585 Datasheet, PDF (258/496 Pages) Microchip Technology – 64/68/80-Pin High-Performance, 64-Kbyte Enhanced Flash Microcontrollers with ECAN Module

PIC18F6585/8585/6680/8680
19.6 A/D Conversions
Figure 19-3 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 19-4 shows the operation of the A/D converter
after the GO bit has been set, the ACQT2:ACQT0 bits
are set to ‘010’ and selecting a 4 TAD acquisition 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).
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.
Note: The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
19.7 Use of the CCP2 Trigger
An A/D conversion can be started by the “special event
trigger” of the CCP2 module. This requires that the
CCP2M3:CCP2M0 bits (CCP2CON<3:0>) be pro-
grammed as ‘1011’ and that the A/D module is enabled
(ADON bit is set). When the trigger occurs, the
GO/DONE bit will be set, starting the A/D conversion
and the Timer1 (or Timer3) counter will be reset to zero.
Timer1 (or Timer3) is reset to automatically repeat the
A/D acquisition period with minimal software overhead
(moving ADRESH/ADRESL to the desired location).
The appropriate analog input channel must be selected
and the minimum acquisition done before the “special
event trigger” sets the GO/DONE bit (starts a
conversion).
If the A/D module is not enabled (ADON is cleared), the
“special event trigger” will be ignored by the A/D
module but will still reset the Timer1 (or Timer3)
counter.
FIGURE 19-3:
A/D CONVERSION TAD CYCLES (ACQT<2:0> = 000, TACQ = 0)
TCY - TAD TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b9 b8 b7 b6 b5 b4 b3 b2 b1 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.
FIGURE 19-4:
A/D CONVERSION TAD CYCLES (ACQT<2:0> = 010, TACQ = 4 TAD)
TACQT Cycles
TAD Cycles
123412345678
Automatic
Acquisition
Time
b9 b8 b7 b6 b5 b4 b3
Conversion starts
(Holding capacitor is disconnected)
9 10 11
b2 b1 b0
Set GO bit
(Holding capacitor continues
acquiring input)
Next Q4: ADRESH:ADRESL is loaded, GO bit is cleared,
ADIF bit is set, holding capacitor is reconnected to analog input.
DS30491C-page 256
 2004 Microchip Technology Inc.