Microchip Technology MA300015 Data Sheet
© 2011 Microchip Technology Inc.
DS70150E-page 141
dsPIC30F6010A/6015
20.1
A/D Result Buffer
The module contains a 16-word dual port, read-only buf-
fer, called ADCBUF0...ADCBUFF, to buffer the A/D
results. The RAM is 10-bits wide, but is read into different
format 16-bit words. The contents of the sixteen A/D
Conversion Result Buffer registers, ADCBUF0 through
ADCBUFF, cannot be written by user software.
fer, called ADCBUF0...ADCBUFF, to buffer the A/D
results. The RAM is 10-bits wide, but is read into different
format 16-bit words. The contents of the sixteen A/D
Conversion Result Buffer registers, ADCBUF0 through
ADCBUFF, cannot be written by user software.
20.2
Conversion Operation
After the A/D module has been configured, the sample
acquisition is started by setting the SAMP bit. Various
sources, such as a programmable bit, timer time-outs and
external events, will terminate acquisition and start a con-
version. When the A/D conversion is complete, the result
is loaded into ADCBUF0...ADCBUFF, and the A/D
Interrupt Flag ADIF and the DONE bit are set after the
number of samples specified by the SMPI bit.
acquisition is started by setting the SAMP bit. Various
sources, such as a programmable bit, timer time-outs and
external events, will terminate acquisition and start a con-
version. When the A/D conversion is complete, the result
is loaded into ADCBUF0...ADCBUFF, and the A/D
Interrupt Flag ADIF and the DONE bit are set after the
number of samples specified by the SMPI bit.
The following steps should be followed for doing an
A/D conversion:
A/D conversion:
1.
Configure the A/D module:
- Configure analog pins, voltage reference
and digital I/O
- Select A/D input channels
- Select A/D conversion clock
- Select A/D conversion trigger
- Turn on A/D module
2.
Configure A/D interrupt (if required):
- Clear ADIF bit
- Select A/D interrupt priority
3.
Start sampling.
4.
Wait the required acquisition time.
5.
Trigger acquisition end, start conversion
6.
Wait for A/D conversion to complete, by either:
- Waiting for the A/D interrupt
7.
Read A/D result buffer, clear ADIF if required.
20.3
Selecting the Conversion
Sequence
Sequence
Several groups of control bits select the sequence in
which the A/D connects inputs to the sample/hold
channels, converts channels, writes the buffer memory,
and generates interrupts. The sequence is controlled
by the sampling clocks.
which the A/D connects inputs to the sample/hold
channels, converts channels, writes the buffer memory,
and generates interrupts. The sequence is controlled
by the sampling clocks.
The SIMSAM bit controls the acquire/convert
sequence for multiple channels. If the SIMSAM bit is
‘0’, the two or four selected channels are acquired and
converted sequentially, with two or four sample clocks.
If the SIMSAM bit is ‘1’, two or four selected channels
are acquired simultaneously, with one sample clock.
The channels are then converted sequentially. Obvi-
ously, if there is only 1 channel selected, the SIMSAM
bit is not applicable.
sequence for multiple channels. If the SIMSAM bit is
‘0’, the two or four selected channels are acquired and
converted sequentially, with two or four sample clocks.
If the SIMSAM bit is ‘1’, two or four selected channels
are acquired simultaneously, with one sample clock.
The channels are then converted sequentially. Obvi-
ously, if there is only 1 channel selected, the SIMSAM
bit is not applicable.
The CHPS bits selects how many channels are sam-
pled. This can vary from 1, 2 or 4 channels. If CHPS
selects 1 channel, the CH0 channel will be sampled at
the sample clock and converted. The result is stored in
the buffer. If CHPS selects 2 channels, the CH0 and
CH1 channels will be sampled and converted. If CHPS
selects 4 channels, the CH0, CH1, CH2 and CH3
channels will be sampled and converted.
pled. This can vary from 1, 2 or 4 channels. If CHPS
selects 1 channel, the CH0 channel will be sampled at
the sample clock and converted. The result is stored in
the buffer. If CHPS selects 2 channels, the CH0 and
CH1 channels will be sampled and converted. If CHPS
selects 4 channels, the CH0, CH1, CH2 and CH3
channels will be sampled and converted.
The SMPI bits select the number of acquisition/conver-
sion sequences that would be performed before an
interrupt occurs. This can vary from 1 sample per
interrupt to 16 samples per interrupt.
sion sequences that would be performed before an
interrupt occurs. This can vary from 1 sample per
interrupt to 16 samples per interrupt.
The user cannot program a combination of CHPS and
SMPI bits that specifies more than 16 conversions per
interrupt, or 8 conversions per interrupt, depending on
the BUFM bit. The BUFM bit, when set, will split the
16-word results buffer (ADCBUF0...ADCBUFF) into
two 8-word groups. Writing to the 8-word buffers will be
alternated on each interrupt event. Use of the BUFM bit
will depend on how much time is available for moving
data out of the buffers after the interrupt, as determined
by the application.
SMPI bits that specifies more than 16 conversions per
interrupt, or 8 conversions per interrupt, depending on
the BUFM bit. The BUFM bit, when set, will split the
16-word results buffer (ADCBUF0...ADCBUFF) into
two 8-word groups. Writing to the 8-word buffers will be
alternated on each interrupt event. Use of the BUFM bit
will depend on how much time is available for moving
data out of the buffers after the interrupt, as determined
by the application.
If the processor can quickly unload a full buffer within
the time it takes to acquire and convert one channel,
the BUFM bit can be ‘0’ and up to 16 conversions may
be done per interrupt. The processor will have one
sample and conversion time to move the sixteen
conversions.
the time it takes to acquire and convert one channel,
the BUFM bit can be ‘0’ and up to 16 conversions may
be done per interrupt. The processor will have one
sample and conversion time to move the sixteen
conversions.
If the processor cannot unload the buffer within the acqui-
sition and conversion time, the BUFM bit should be ‘1’.
For example, if SMPI<3:0> (ADCON2<5:2> = 0111),
then eight conversions will be loaded into 1/2 of the buf-
fer, following which an interrupt occurs. The next eight
conversions will be loaded into the other 1/2 of the buffer.
The processor will have the entire time between
interrupts to move the eight conversions.
sition and conversion time, the BUFM bit should be ‘1’.
For example, if SMPI<3:0> (ADCON2<5:2> = 0111),
then eight conversions will be loaded into 1/2 of the buf-
fer, following which an interrupt occurs. The next eight
conversions will be loaded into the other 1/2 of the buffer.
The processor will have the entire time between
interrupts to move the eight conversions.
The ALTS bit can be used to alternate the inputs
selected during the sampling sequence. The input
multiplexer has two sets of sample inputs: MUX A and
MUX B. If the ALTS bit is ‘0’, only the MUX A inputs are
selected for sampling. If the ALTS bit is ‘1’ and
SMPI<3:0> = 0000, on the first sample/convert
sequence, the MUX A inputs are selected, and on the
next acquire/convert sequence, the MUX B inputs are
selected.
selected during the sampling sequence. The input
multiplexer has two sets of sample inputs: MUX A and
MUX B. If the ALTS bit is ‘0’, only the MUX A inputs are
selected for sampling. If the ALTS bit is ‘1’ and
SMPI<3:0> = 0000, on the first sample/convert
sequence, the MUX A inputs are selected, and on the
next acquire/convert sequence, the MUX B inputs are
selected.
The CSCNA bit (ADCON2<10>) will allow the CH0
channel inputs to be alternately scanned across a
selected number of analog inputs for the MUX A group.
The inputs are selected by the ADCSSL register. If a
particular bit in the ADCSSL register is ‘1’, the corre-
sponding input is selected. The inputs are always
scanned from lower to higher numbered inputs, starting
after each interrupt. If the number of inputs selected is
greater than the number of samples taken per interrupt,
the higher numbered inputs are unused.
channel inputs to be alternately scanned across a
selected number of analog inputs for the MUX A group.
The inputs are selected by the ADCSSL register. If a
particular bit in the ADCSSL register is ‘1’, the corre-
sponding input is selected. The inputs are always
scanned from lower to higher numbered inputs, starting
after each interrupt. If the number of inputs selected is
greater than the number of samples taken per interrupt,
the higher numbered inputs are unused.