the ATM external counter value is compared to the ATCV[15:0] register value. Based on
the comparison result, the ATM trim bit under test will get cleared or stay asserted. This
is done until all trim bits have been tested by ATM SAR machine.
Before the ATM can be enabled, the ATM expected count needs to be derived and stored
into the ATCV register. The ATCV expected count is derived based on the required
target Internal Reference Clock (IRC) frequency, and the frequency of the external
reference clock using the following formula:
ATCV
• Fr = Target Internal Reference Clock (IRC) Trimmed Frequency
• Fe = External Clock Frequency
If the auto trim is being performed on the 4 MHz IRC, the calculated expected count
value must be multiplied by 128 before storing it in the ATCV register. Therefore, the
ATCV Expected Count Value for trimming the 4 MHz IRC is calculated using the
following formula.
(128)
25.5 Initialization / Application information
This section describes how to initialize and configure the MCG module in an application.
The following sections include examples on how to initialize the MCG and properly
switch between the various available modes.
25.5.1 MCG module initialization sequence
The MCG comes out of reset configured for FEI mode.
The internal reference will stabilize in t
irefsts
microseconds before the FLL can acquire
lock. As soon as the internal reference is stable, the FLL will acquire lock in t
fll_acquire
milliseconds.
Initialization / Application information
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
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Freescale Semiconductor, Inc.
