Basic Features and Usage of the ADC
697
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Analog To Digital Converter (ADC) Module
With conversions ongoing in continuous conversion mode, if the MODE field of a group is cleared, then
that group switches to the single conversion sequence mode. Conversions for this group will stop once all
channels selected for that group have been converted.
19.3.6 How to Start a Conversion
The conversion groups Group1 and Group2 are software-triggered by default. A conversion in these
groups can be started just by writing the desired channels to the respective Channel-Select Registers. For
example, in order to convert channels 0, 1, 2, and 3 in Group1 and channels 8, 9, 10, and 11 in Group2,
the application just has to write 0x0000000F to ADG1SEL and 0x00000F00 to ADG2SEL. The ADC
module will start by servicing the group that was triggered first, Group1 in this example.
The conversions for all groups are performed in ascending order of the channel number. For the Group1
the conversions will be performed in the order: channel 0 first, followed by channel 1, then channel 2, and
then channel 3. The Group2 conversions will be performed in the order: channels 8, 9, 10, and 11.
The Event Group is only hardware-triggered. There are up to eight hardware event trigger sources defined
for the ADC module. Check the device datasheet for a complete listing of these eight hardware trigger
options.
The trigger source to be used needs to be configured in the ADEVSRC register. Similar registers also
exist for the Group1 and Group2 as these can also be configured to be event-triggered.
The polarity of the event trigger is also configurable, with a falling edge being the default.
An Event Group conversion starts when at least one channel is selected for conversion in this group, and
when the defined event trigger occurs.
If any conversion group is configured to be in a continuous conversion mode, then it needs to only be
triggered once. All the channels selected for conversion in that group will be converted repeatedly.
19.3.7 How to Know When the Group Conversion is Completed
Each conversion group has a status flag to indicate when its conversion has ended. See ADEVSR,
ADG1SR, and ADG2SR. This bit is set when a conversion sequence for a group ends. This bit does is
always set if a group is configured for continuous conversions.
19.3.8 How Results are Stored in the Results’ Memory
The ADC stores the conversion results in three separate memory regions in the ADC Results’ RAM, one
region for each group. Each memory region is a stack of buffers, with each buffer capable of holding one
conversion result. The number of buffers allocated for each group is programmed by configuring the ADC
module registers ADBNDCR and ADBNDEND.
ADBNDCR contains two 9-bit pointers BNDA and BNDB. BNDA, BNDB, and BNDEND are used to
partition the total memory available into three memory regions as shown in
. Both BNDA and
BNDB are pointers referenced from the start of the results’ memory. BNDA specifies the number of buffers
allocated for the Event Group conversion results in units of two buffers; BNDB specifies the number of
buffers allocated for the Event Group plus Group1 in units of two buffers. Please refer to
for more details on configuring the ADC results’ memory.
ADBNDEND contains a 3-bit field called BNDEND that configures the total memory available. The ADC
module can support up to 1024 buffers. The device supports a maximum of 64 buffers for both the ADC
modules.
