Configuring the Tracking Time
When burst mode is disabled, the ADTM bit controls the ADC track-and-hold mode. In its default state the ADC input is continuously
tracked, except when a conversion is in progress. A conversion will begin immediately when the start-of-conversion trigger occurs.
When the ADTM bit is logic 1, each conversion is preceded by a tracking period of 4 SAR clocks (after the start-of-conversion signal)
for any internal conversion trigger source. When the CNVSTR signal is used to initiate conversions with ADTM set to 1, ADC0 tracks
only when CNVSTR is low; conversion begins on the rising edge of CNVSTR. Setting ADTM to 1 is primarily useful when AMUX set-
tings are frequently changed and conversions are started using the ADBUSY bit.
Write '1' to ADBUSY,
Timer Overflow
ADTM = 1
Track
Convert
Low Power Mode
ADTM = 0
Track or
Convert
Convert
Track
Low Power
or Convert
SAR
Clocks
SAR
Clocks
B. ADC0 Timing for Internal Trigger Source
1 2 3 4 5 6 7 8 9
CNVSTR
ADTM = 1
A. ADC0 Timing for External Trigger Source
SAR Clocks
Track or Convert
Convert
Track
ADTM = 0
Track
Convert
Low Power
Mode
Low Power
or Convert
10 11 12 13 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Figure 13.3. Track and Conversion Example Timing (Normal, Non-Burst Operation)
When burst mode is enabled, additional tracking times may need to be specified. Because burst mode may power the ADC on from an
unpowered state and take multiple conversions for each start-of-conversion source, two additional timing fields are provided. If the ADC
is powered down when the burst sequence begins, it will automatically power up and wait for the time specified in the ADPWR bit field.
If the ADC is already powered on, tracking depends solely on ADTM for the first conversion. The ADTK field determines the amount of
tracking time given to any subsequent samples in burst mode—essentially, ADTK specifies how long the ADC will wait between burt-
mode conversions. If ADTM is set, an additional 4 SAR clocks will be added to the tracking phase of all conversions in burst mode.
EFM8SB2 Reference Manual
Analog-to-Digital Converter (ADC0)
silabs.com
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