Microchip Technology dsPIC30F - How to Start Sampling

© 2004 Microchip Technology Inc. DS70064C-page 17-17
Section 17. 10-bit A/D Converter
10-bit A/D
Converter
17
17.10.2 Simultaneous Sampling Enable
Some applications may require that multiple signals are sampled at the exact same time
instance. The SIMSAM control bit (ADCON1<3>) works in conjunction with the CHPS control
bits and controls the sample/convert sequence for multiple channels as shown in Table 17-1. The
SIMSAM control bit has no effect on the module operation if CHPS<1:0> = 00. If more than one
S/H amplifier is enabled by the CHPS control bits and the SIMSAM bit is ‘0’, the two or four
selected channels are sampled and converted sequentially with two or four sampling periods. If
the SIMSAM bit is ‘1’, two or four selected channels are sampled simultaneously with one
sampling period. The channels are then converted sequentially.
Table 17-1: Sample/Conversion Control Options
17.11 How to Start Sampling
17.11.1 Manual
Setting the SAMP bit (ADCON1<1>) causes the A/D to begin sampling. One of several options
can be used to end sampling and complete the conversions. Sampling will not resume until the
SAMP bit is once again set. For an example, see Figure 17-4.
17.11.2 Automatic
Setting the ASAM bit (ADCON1<2>) causes the A/D to automatically begin sampling a channel
whenever a conversion is not active on that channel. One of several options can be used to end
sampling and complete the conversions. If the SIMSAM bit specifies sequential sampling,
sampling on a channel resumes after the conversion of that channel completes. If the SIMSAM
bit specifies simultaneous sampling, sampling on a channel resumes after the conversion of all
channels completes. For an example, see Figure 17-5.
CHPS<1:0> SIMSAM Sample/Conversion Sequence
# of Sample/
Convert Cycles
to Complete
Example
00 x Sample CH0, Convert CH0 1 Figure 17-4,
Figure 17-5,
Figure 17-6,
Figure 17-7,
Figure 17-10,
Figure 17-11,
Figure 17-14,
Figure 17-15
01 0 Sample CH0, Convert CH0
Sample CH1, Convert CH1
2
1x 0 Sample CH0, Convert CH0
Sample CH1, Convert CH1
Sample CH2, Convert CH2
Sample CH3, Convert CH3
4 Figure 17-9,
Figure 17-13,
Figure 17-20
01 1 Sample CH0, CH1 simultaneously
Convert CH0
Convert CH1
1 Figure 17-18
1x 1 Sample CH0, CH1, CH2, CH3
simultaneously
Convert CH0
Convert CH1
Convert CH2
Convert CH3
1 Figure 17-8
Figure 17-12,
Figure 17-16,
Figure 17-17,
Figure 17-9,