dsPIC30F Family Reference Manual
DS70064C-page 17-12 © 2004 Microchip Technology Inc.
A sample/convert sequence that uses multiple S/H channels can be simultaneously sampled or
sequentially sampled, as controlled by the SIMSAM bit (ADCON1<3>). Simultaneously sampling
multiple signals ensures that the snapshot of the analog inputs occurs at precisely the same time
for all inputs. Sequential sampling takes a snapshot of each analog input just before conversion
starts on that input, and the sampling of multiple inputs is not correlated.
Figure 17-3: Simultaneous and Sequential Sampling
The start time for sampling can be controlled in software by setting the SAMP control bit. The
start of the sampling time can also be controlled automatically by the hardware. When the A/D
converter operates in the Auto-Sample mode, the S/H amplifier(s) is reconnected to the the
analog input pin at the end of the conversion in the sample/convert sequence. The auto-sample
function is controlled by the ASAM control bit (ADCON1<2>).
The conversion trigger source ends the sampling time and begins an A/D conversion or a
sample/convert sequence. The conversion trigger source is selected by the SSRC control bits.
The conversion trigger can be taken from a variety of hardware sources, or can be controlled
manually in software by clearing the SAMP control bit. One of the conversion trigger sources is
an auto-conversion. The time between auto-conversions is set by a counter and the A/D clock.
The Auto-Sample mode and auto-conversion trigger can be used together to provide endless
automatic conversions without software intervention.
An interrupt may be generated at the end of each sample/convert sequence or multiple
sample/convert sequences as determined by the value of the SMPI control bits ADCON2<5:2>.
The number of sample/convert sequences between interrupts can vary between 1 and 16. The
user should note that the A/D conversion buffer holds 16 results when the SMPI value is selected.
The total number of conversion results between interrupts is the product of the channels per
sample and the SMPI value. The total number of conversions between interrupts should not
exceed the buffer length.
AN0
AN1
AN2
AN3
Simultaneous
Sampling
Sequential
Sampling
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