Cypress FM4 Series - High-Speed CR Trimming Function Usage Precautions

CHAPTER 2-3: High-Speed CR Trimming
FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E 129
6. High-Speed CR Trimming Function Usage Precautions
This section explains the precautions for using the high-speed CR trimming function.
 Low-speed CR oscillator
This trimming function is only enabled for the high-speed CR oscillator.
It cannot apply to the low-speed CR oscillator.
 Data stored in the CR trimming area
The CR trimming" area stores the factory preset frequency trimming data. For the address of the "CR
trimming" area, see Flash Programming Manual for the product used.
When Data in flash memory is erased, the data in “CR trimming” area is also erase at the same time. To
use the data in the CR trimming area, save the data in the CR trimming area to other area such as RAM
before erasing the data in flash memory.
Otherwise, erase the sectors other than those in CR trimming area.
 For accuracy of oscillation frequency of High-speed CR oscillator
Without setting High-speed CR oscillation temperature trimming register (MCR_TTRM) and High-speed
CR oscillation frequency trimming register (MCR_FTRM), the accuracy of the High-speed CR oscillator
described in Data Sheet cannot be guaranteed. So, be sure to set the above registers before use.
 How to use base timer
For information about how to use base timer, see Chapters Base Timer in Timer Part and I/O Port.
 FCS (Anomalous Frequency Detection)
For FCS function (anomalous frequency detection), see Chapter "Clock supervisor". Do not perform CR
trimming after the FCS function is enabled.