mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 396

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Multipurpose Clock Generator (MCGV3)
16.5.4
The IRC is calibrated by writing to the MCGTRM register first, then using the FTRIM bit to “fine tune”
the frequency. We will refer to this total 9-bit value as the trim value, ranging from 0x000 to 0x1FF, where
the FTRIM bit is the LSB.
The trim value after reset is the factory trim value unless the device resets into any BDM mode in which
case it is 0x800. Writing a larger value will decrease the frequency and smaller values will increase the
frequency. The trim value is linear with the period, except that slight variations in wafer fab processing
produce slight non-linearities between trim value and period. These non-linearities are why an iterative
16-28
Calibrating the Internal Reference Clock (IRC)
Figure 16-12. Flowchart of BLPI to FEE Mode Transition using an 8 MHz crystal
MCGC2 = $36
MCGC1 = $18
OSCINIT = 1 ?
MCGC2 = $00
I
CHECK LOCK
N BLPI MODE
CHECK
OPTIONAL:
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
START
= 1?
YES
YES
NO
NO
CLKST = %00?
IREFST = 0?
CHECK LOCK
IN FEE MODE
OPTIONAL:
CONTINUE
CHECK
CHECK
= 1?
YES
YES
YES
NO
NO
NO
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