The ADC module has the capability of automatically averaging the result of multiple
conversions. The hardware average function is enabled by setting SC3[AVGE] and
operates in any of the conversion modes and configurations.
NOTE
For the chip specific modes of operation, see the power
management information of this MCU.
33.4.1 Clock select and divide control
One of four clock sources can be selected as the clock source for the ADC module.
This clock source is then divided by a configurable value to generate the input clock
ADCK, to the module. The clock is selected from one of the following sources by means
of CFG1[ADICLK].
• Bus clock. This is the default selection following reset.
• ALTCLK2: As defined for this MCU. See the chip configuration information.
Conversions are possible using ALTCLK2 as the input clock source while the MCU
is in Normal Stop mode.
• ALTCLK: As defined for this MCU. See the chip configuration information.
Conversions are possible using ALTCLK as the input clock source while the MCU is
in Normal Stop mode.
• Asynchronous clock (ADACK): This clock is generated from a clock source within
the ADC module. When the ADACK clock source is selected, it is not required to be
active prior to conversion start. When it is selected and it is not active prior to a
conversion start CFG2[ADACKEN]=0, ADACK is activated at the start of a
conversion and deactivated when conversions are terminated. In this case, there is an
associated clock startup delay each time the clock source is re-activated. To avoid the
conversion time variability and latency associated with the ADACK clock startup, set
CFG2[ADACKEN]=1 and wait the worst-case startup time of 5 µs prior to initiating
any conversions using the ADACK clock source. Conversions are possible using
ADACK as the input clock source while the MCU is in Normal Stop mode. See
for more information.
Whichever clock is selected, its frequency must fall within the specified frequency range
for ADCK. If the available clocks are too slow, the ADC may not perform according to
specifications. If the available clocks are too fast, the clock must be divided to the
appropriate frequency. This divider is specified by CFG1[ADIV] and can be divide-by 1,
2, 4, or 8.
Functional description
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
718
Freescale Semiconductor, Inc.
