70592C Datasheet, PDF (209/314 Pages) Microchip Technology – High-Performance, 16-bit Microcontrollers

PIC24HJXXXGPX06A/X08A/X10A
20.0 10-BIT/12-BIT
ANALOG-TO-DIGITAL
CONVERTER (ADC)
Note 1: This data sheet summarizes the features
of the PIC24HJXXXGPX06A/X08A/X10A
family of devices. However, it is not
intended to be a comprehensive refer-
ence source. To complement the infor-
mation in this data sheet, refer to the
“dsPIC33F/PIC24H Family Reference
Manual”, Section 16. “Analog-to-Digital
Converter (ADC)” (DS70225), which is
available from the Microchip website
(www.microchip.com).
2: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.
The PIC24HJXXXGPX06A/X08A/X10A devices have
up to 32 Analog-to-Digital input channels. These
devices also have up to 2 Analog-to-Digital converter
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.
Note: The ADC module needs to be disabled
before modifying the AD12B bit.
20.1 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
• Two result alignment options (signed/unsigned)
• 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.
© 2011 Microchip Technology Inc.
Depending on the particular device pinout, the Ana-
log-to-Digital Converter 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 Analog-to-Digital Converter is
shown in Figure 20-1.
20.2 Analog-to-Digital 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 the ADC module (ADxCON1<15>)
2. Configure ADC interrupt (if required):
a) Clear the ADxIF bit
b) Select ADC interrupt priority
20.3 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, the
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.
DS70592C-page 209