dsPIC30F Family Reference Manual
DS70064C-page 17-24 © 2004 Microchip Technology Inc.
17.12.3 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.
17.12.3.1 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.
17.12.3.2 GP 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.
17.12.3.3 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.
17.12.3.4 Synchronizing A/D Operations to Internal or External Events
Using the modes where an external event trigger pulse ends sampling and starts conversion
(SSRC = 001, 10, 011) may be used in combination with auto-sampling (ASAM = 1) to cause
the A/D to synchronize the sample conversion events to the trigger pulse source. For example,
in Figure 17-11 where SSRC = 010 and ASAM = 1, the A/D will always end sampling and start
conversions synchronously with the timer compare trigger event. The A/D will have a sample
conversion rate that corresponds to the timer comparison event rate. See Example 17-6 for code
example.
Figure 17-10: Converting 1 Channel, Manual Sample Start, Conversion Trigger Based Conversion Start
Conversion
ADCLK
SAMP
ADCBUF0
TSAMP
TCONV
BSF ADCON1,SAMP
Instruction Execution
Trigger
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