AN3137 datasheet(12/42 Pages) STMICROELECTRONICS

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STM8L/STM8AL ADC internal hardware

AN3137

12/42

Doc ID 16983 Rev 3

1.7

Conversion triggers

ADC conversion can start when a trigger occurs. Three main sources of trigger can be

selected:

●

software trigger (writing to one register bit)

●

timer trigger (if a timer event occurs)

●

external trigger (change of the state of a dedicated I/O pin)

1.8

Analog watchdog feature

This function is used to monitor converted values on selected channels. If the converted

value on a given ADC input channel is outside the reference voltage threshold, the analog

watchdog flag (AWD) bit is set and can generate an interrupt.

1.9

Interrupt generation

The ADC can generate an interrupt if some events occur. This simplifies the programming

and speeds up the ADC service routines.

The interrupt sources are the following ones:

●

end of conversion (when an ADC data register is filled with a new value)

●

analog watchdog event (if the ADC converted value is outside a given voltage range)

●

overrun event (when, after a conversion, a second conversion is complete and the DMA

has not read the first conversion value yet)

1.10

DMA transfer

The ADC can be programmed to use the built-in DMA to transfer converted ADC data to the

memory. This speeds up the data collection (instead of ADC data register polling by the

CPU, the DMA transfer runs in the background) when the CPU is performing another

operation. Refer to the STM8L05xx, STM8L15xx, STM8L162x, STM8AL31xx and

STM8AL3Lxxx microcontroller family reference manual (RM0031) for a description of DMA

operation. Using the DMA transfer is especially useful in long data array collection (voice,

signal processing,...).

1.11

Sampling modes

The ADC can operate in three modes which mainly differ in the way converted input

channels are managed:

●

single mode (one conversion and then ADC stops)

●

continuous mode (ADC continues conversion to the next channel)

●

scan mode (ADC converts a set of selected channels to the memory)

These modes are described in Section 2: STM8L/STM8AL ADC usage/programming.

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