© 2004 Microchip Technology Inc. DS70065C-page 18-17
Section 18. 12-bit A/D Converter
12-bit A/D
Converter
18
18.11.2.1 Free Running Sample Conversion Sequence
As shown in Figure 18-6, using the Auto-Convert Conversion Trigger mode (SSRC = 111) in
combination with the Auto-Sample Start mode (ASAM = 1) allows the A/D module to schedule
sample/conversion sequences with no intervention by the user or other device resources. This
“Clocked” mode allows continuous data collection after module initialization.
Figure 18-6: Converting 1 Channel, Auto-Sample Start, T
AD Based Conversion Start
18.11.2.2 Sample Time Considerations Using Clocked Conversion Trigger and Automatic Sampling
The user must ensure the sampling time exceeds the sampling requirements as outlined in
Section 18.15 “A/D Sampling Requirements”.
Assuming that the module is set for automatic sampling and using a clocked conversion trigger,
the sampling interval is specified by the SAMC bits.
18.11.3 Event Trigger Conversion Start
It is often desirable to synchronize the end of sampling and the start of conversion with some
other time event. The A/D module may use one of three sources as a conversion trigger event.
18.11.3.1 External INT Pin Trigger
When SSRC<2:0> = 001, the A/D conversion is triggered by an active transition on the INT0 pin.
The INT0 pin may be programmed for either a rising edge input or a falling edge input.
18.11.3.2 General Purpose Timer Compare Trigger
The A/D is configured in this Trigger mode by setting SSRC<2:0> = 010. When a match occurs
between the 32-bit timer TMR3/TMR2 and the 32-bit Combined Period register PR3/PR2, a
special ADC trigger event signal is generated by Timer3. This feature does not exist for the
TMR5/TMR4 timer pair. Refer to Section 12. “Timers” for more details.
18.11.3.3 Motor Control PWM Trigger
The PWM module has an event trigger that allows A/D conversions to be synchronized to the
PWM time base. When SSRC<2:0> = 011, the A/D sampling and conversion times occur at any
user programmable point within the PWM period. The special event trigger allows the user to
minimize the delay between the time when A/D conversion results are acquired and the time
when the duty cycle value is updated. Refer to Section 15. “Motor Control PWM” for more
details.
ADCLK
SAMP
ADCBUF1
TSAMP TCONV
DONE
TSAMP
TCONV
ADCBUF0
BSF ADCON1,ASAM
Instruction Execution
Reset by
software
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