Datasheet

© 2009 Microchip Technology Inc. DS70286C-page 225
dsPIC33FJXXXGPX06/X08/X10
21.0 10-BIT/12-BIT
ANALOG-TO-DIGITAL
CONVERTER (ADC)
The dsPIC33FJXXXGPX06/X08/X10 devices have up
to 32 ADC input channels. These devices also have up
to 2 ADC modules (ADCx, where ‘x’ = 1 or 2), each with
its own set of Special Function Registers.
The AD12B bit (ADxCON1<10>) allows each of the
ADC modules to be configured by the user as either a
10-bit, 4-sample/hold ADC (default configuration) or a
12-bit, 1-sample/hold ADC.
21.1 Key Features
The 10-bit ADC configuration has the following key
features:
• Successive Approximation (SAR) conversion
• Conversion speeds of up to 1.1 Msps
• Up to 32 analog input pins
• External voltage reference input pins
• Simultaneous sampling of up to four analog input
pins
• Automatic Channel Scan mode
• Selectable conversion trigger source
• Selectable Buffer Fill modes
• Four result alignment options (signed/unsigned,
fractional/integer)
• Operation during CPU Sleep and Idle modes
The 12-bit ADC configuration supports all the above
features, except:
• In the 12-bit configuration, conversion speeds of
up to 500 ksps are supported
• There is only 1 sample/hold amplifier in the 12-bit
configuration, so simultaneous sampling of
multiple channels is not supported.
Depending on the particular device pinout, the ADC
can have up to 32 analog input pins, designated AN0
through AN31. In addition, there are two analog input
pins for external voltage reference connections. These
voltage reference inputs may be shared with other
analog input pins. The actual number of analog input
pins and external voltage reference input configuration
will depend on the specific device. Refer to the device
data sheet for further details.
A block diagram of the ADC is shown in Figure 21-1.
21.2 ADC Initialization
The following configuration steps should be performed.
1. Configure the ADC module:
a) Select port pins as analog inputs
(ADxPCFGH<15:0> or ADxPCFGL<15:0>)
b) Select voltage reference source to match
expected range on analog inputs
(ADxCON2<15:13>)
c) Select the analog conversion clock to
match desired data rate with processor
clock (ADxCON3<7:0>)
d) Determine how many S/H channels will be
used (ADxCON2<9:8> and
ADxPCFGH<15:0> or ADxPCFGL<15:0>)
e) Select the appropriate sample/conversion
sequence (ADxCON1<7:5> and
ADxCON3<12:8>)
f) Select how conversion results are
presented in the buffer (ADxCON1<9:8>)
g) Turn on ADC module (ADxCON1<15>)
2. Configure ADC interrupt (if required):
a) Clear the ADxIF bit
b) Select ADC interrupt priority
21.3 ADC and DMA
If more than one conversion result needs to be buffered
before triggering an interrupt, DMA data transfers can
be used. Both ADC1 and ADC2 can trigger a DMA data
transfer. If ADC1 or ADC2 is selected as the DMA IRQ
source, a DMA transfer occurs when the AD1IF or
AD2IF bit gets set as a result of an ADC1 or ADC2
sample conversion sequence.
The SMPI<3:0> bits (ADxCON2<5:2>) are used to
select how often the DMA RAM buffer pointer is
incremented.
The ADDMABM bit (ADxCON1<12>) determines how
the conversion results are filled in the DMA RAM buffer
area being used for ADC. If this bit is set, DMA buffers
are written in the order of conversion. The module will
provide an address to the DMA channel that is the
same as the address used for the non-DMA
stand-alone buffer. If the ADDMABM bit is cleared, then
DMA buffers are written in Scatter/Gather mode. The
module will provide a scatter/gather address to the
DMA channel, based on the index of the analog input
and the size of the DMA buffer.
Note: This data sheet summarizes the features
of the dsPIC33FJXXXGPX06/X08/X10
family of devices. However, it is not
intended to be a comprehensive reference
source. To complement the information in
this data sheet, refer to Section 16.
“Analog-to-Digital Converter (ADC)”
(DS70183) in the “dsPIC33F Family
Reference Manual”, which is available
from the Microchip web site
(www.microchip.com).
Note: The ADC module needs to be disabled
before modifying the AD12B bit.