ST STM32 Nucleo Installation and operating instructions

March 2010 Doc ID 16840 Rev 1 1/18
AN3116
Application note
STM32™’s ADC modes
and their applications
Introduction
STM32 microcontrollers have one of the most advanced ADCs on the microcontroller
market. You could imagine a multitude of applications based on the STM32 ADC features.
Some ADC modes are provided to simplify measurements and give efficient results in
applications such as motor control.
This application note provides help for ADC users to understand some advanced modes
offered in the STM32 microcontrollers, and to quick start development. Each of the
described modes is provided with an example of application to better understand how to use
them. Most modes come with a basic firmware to make it easier to understand the ADC
configuration.
This application note is divided into two sections: independent modes and dual modes. The
first section describes modes used with a single ADC. The second section describes modes
that should be used with two ADCs (ADC1 and ADC2 working jointly).
This application note does not describe the ADC modes that result from the combination of
other modes.
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Contents AN3116
2/18 Doc ID 16840 Rev 1
Contents
1 Independent modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Single-channel, single conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Multichannel (scan), single conversion mode . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Single-channel continuous conversion mode . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2 Example of applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Multichannel (scan) continuous conversion mode . . . . . . . . . . . . . . . . . . . 7
1.4.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5 Injected conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Dual modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Dual regular simultaneous mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Dual fast interleaved mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Dual slow interleaved mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Dual alternate trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5 Dual combined regular/injected simultaneous mode . . . . . . . . . . . . . . . . 14
2.5.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

AN3116 Contents
Doc ID 16840 Rev 1 3/18
2.6 Dual combined: injected simultaneous + interleaved mode . . . . . . . . . . . 14
2.6.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.6.2 Example of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

List of figures AN3116
4/18 Doc ID 16840 Rev 1
List of figures
Figure 1. Single-channel, single conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. ADC sequencer converting 7 channels with different configured sampling
times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3. Multichannel, single conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4. Single-channel, continuous conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 5. Multichannel, continuous conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 6. Injected conversion mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 7. Dual regular simultaneous mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 8. Simultaneous measurement of voltage and current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 9. Dual fast interleaved mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 10. Dual slow interleaved mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 11. Dual alternate trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 12. Dual combined regular/injected simultaneous mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 13. Dual combined: injected simultaneous + interleaved mode . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 14. UPS system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

AN3116 Independent modes
Doc ID 16840 Rev 1 5/18
1 Independent modes
1.1 Single-channel, single conversion mode
1.1.1 Description
This is the simplest ADC mode. In this mode, the ADC performs the single conversion
(single sample) of a single channel x (refer to Figure 1.) and stops after completion of the
conversion.
Note: This application note is not delivered with a firmware example of this mode.
Figure 1. Single-channel, single conversion mode
1.1.2 Example of application
This mode can be used for the measurement of a voltage level to decide if the system can
be started or not. Measure the voltage level of the battery before starting the system: if the
battery has a low level, the “low battery” message appears. In this case, do not start the
system.
1.2 Multichannel (scan), single conversion mode
1.2.1 Description
This mode is used to convert some channels successively in independent mode. With the
ADC sequencer, you can use this ADC mode to configure any sequence of up to 16
channels successively with different sampling times and in different orders. You can for
example carry out the sequence shown in Figure 2. In this way, you do not have to stop the
ADC during the conversion process in order to reconfigure the next channel with a different
sampling time. This mode saves additional CPU load and heavy software development.
Figure 2. ADC sequencer converting 7 channels with different configured sampling
times
Note: This application note is not delivered with a firmware example of this mode.
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Independent modes AN3116
6/18 Doc ID 16840 Rev 1
Figure 3. Multichannel, single conversion mode
1.2.2 Example of application
This mode can be used when starting a system depends on some parameters like knowing
the coordinates of the arm’s tip in a manipulator arm system. In this case, you have to read
the position of each articulation in the manipulator arm system at power-on to determine the
coordinates of the arm’s tip.
This mode can also be used to make single measurements of multiple signal levels (voltage,
pressure, temperature, etc.) to decide if the system can be started or not in order to protect
the people and equipment.
It can likewise be used to convert signals coming from strain gauges to determine the
directions and values of the different strains and deformations of an object.
1.3 Single-channel continuous conversion mode
1.3.1 Description
The single-channel continuous conversion mode converts a single channel continuously
and indefinitely in regular channel conversion.
The continuous mode feature allows the ADC to work in the background. The ADC converts
the channels continuously without any intervention from the CPU. Additionally, the DMA can
be used in circular mode, thus reducing the CPU load.
Note: An example of firmware is provided with this application note: SingleChannelContinuous.
The example uses two methods: DMA and interrupts. To select either method, simply
comment or uncomment #define USE_DMA_Transfer in the main.c file.
Figure 4. Single-channel, continuous conversion mode
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AN3116 Independent modes
Doc ID 16840 Rev 1 7/18
1.3.2 Example of applications
This ADC mode can be implemented to monitor a battery voltage, the measurement and
regulation of an oven temperature, etc.
In the case of the oven temperature regulation, the temperature is read and compared to the
temperature set by the user. When the oven temperature reaches the desired temperature,
the heating resistor is powered off.
1.4 Multichannel (scan) continuous conversion mode
1.4.1 Description
The multichannel, or scan, continuous mode can be used to convert some channels
successively with the ADC in independent mode. With the sequencer, you can configure any
sequence of up to 16 channels successively with different sampling times and different
orders. This mode is similar to the multichannel single conversion mode except that it does
not stop converting after the last channel of the sequence but it restarts the conversion
sequence from the first channel and continues indefinitely.
Figure 5. Multichannel, continuous conversion mode
1.4.2 Example of application
This mode can be used to monitor multiple voltages and temperatures in a multiple battery
charger. The voltage and temperature of each battery are read during the charging process.
When the voltage or the temperature reaches the maximum level, the corresponding battery
should be disconnected from the charger.
1.5 Injected conversion mode
1.5.1 Description
This mode is intended for use when conversion is triggered by an external event or by
software.
The injected group has priority over the regular channel group. It interrupts the conversion of
the current channel in the regular channel group.
Note: An example of firmware is provided with this application note: Indep_InjectedGroup.
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Independent modes AN3116
8/18 Doc ID 16840 Rev 1
Figure 6. Injected conversion mode
1.5.2 Example of application
This mode can be used to synchronize the conversion of channels to an event. It is
interesting in motor control applications where transistor switching generates noise that
impacts ADC measurements and results in wrong conversions. Using a timer, the injected
conversion mode can thus be implemented to delay the ADC measurements to after the
transistor switching.
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AN3116 Dual modes
Doc ID 16840 Rev 1 9/18
2 Dual modes
Dual modes are available in STM32 microcontrollers that feature two ADCs: ADC1 master
and ADC2 slave. ADC1 and ADC2 triggers are synchronized internally for regular and
injected channel conversion. ADC1 and ADC2 work together.
In some devices, there are up to 3 ADCs: ADC1, ADC2 and ADC3. In this case ADC3
always works independently, and is not synchronized with the other ADCs.
Note: Do not sample the same channel on the two ADCs at the same time, this would introduce
conversion errors.
2.1 Dual regular simultaneous mode
2.1.1 Description
The dual regular simultaneous ADC mode is used to perform two conversions
simultaneously owing to the synchronization of ADC1 and ADC2. Each ADC converts a
channel sequence (with scan enabled and the sequencer of each ADC configured) or
converts a single channel (scan disabled). The conversion can be started with an external
trigger or by software. In this mode, the conversion results of ADC1 and ADC2 are stored in
ADC1’s data register (32-bit format). Figure 7 shows how ADC1 and ADC2 convert two
sequences simultaneously. ADC1 converts a sequence of 16 channels successively:
channel 15 to channel 0 and ADC2 converts a sequence of 16 channels successively:
channel 0 to channel 15.
Note: This application note does not provide a firmware example. However the STM32 firmware
library provides an example of this mode at the following path:
\Project\STM32F10x_StdPeriph_Examples\ADC\RegSimul_DualMode.
Figure 7. Dual regular simultaneous mode
2.1.2 Example of application
The dual regular simultaneous mode can be used in applications where two signals should
be sampled and converted at the same time. For example, to measure and plot the single-
phase or three-phase instantaneous electrical power: pn(t) = un(t) × in(t).
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Dual modes AN3116
10/18 Doc ID 16840 Rev 1
In this case, the voltage and current should be measured simultaneously and then the
instantaneous power, which is the product of un(t) and in(t), should be computed.
Figure 8 shows how to measure a power using the two ADCs in dual regular simultaneous
mode.
To measure a single-phase power, ADC1 and ADC2 are used with two channels (1 channel
for the voltage and 1 channel for the current).
To measure a three-phase power, ADC1 and ADC2 are used with 6 channels (3 channels
for the voltage and 3 channels for the current).
Figure 8. Simultaneous measurement of voltage and current
2.2 Dual fast interleaved mode
2.2.1 Description
The dual fast interleaved ADC mode is intended for the conversion of one channel. ADC1
and ADC2 convert the selected channel alternately with a period of 7 ADC clock cycles.
This means that the channel is converted every 7 clock cycles. Each ADC converts the
channel every 14 ADC clock cycles. With a 14 MHz ADC clock, it is thus possible to reach
2 Msamples per second: 14 MHz/7 = 2 MHz (sampling frequency). The conversion can be
started by external trigger or by software and the conversion results of ADC1 and ADC2 are
stored into ADC1 data register (32-bit format).
The maximum allowed sampling time is 7 ADC clock cycles to avoid the overlap between
the ADC1 and ADC2 sampling phases in the event that they convert the same channel. This
means that the only allowed sampling time is 1.5 cycles.
Note: 1 It is highly recommended to use DMA instead of interrupts to avoid the loss of data.
2 An example of firmware is provided with this application note: Dual_FastInterleaved.
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