Part Number:MSP430F5335
I am working on adding temperature compensation and calibration support for the RTC_B peripheral on the MSP430F5335. There are a couple of spots that I have questions about in the October 2016 revision of the Users's Guide:
1) 23.2.5 Real-Time Clock Calibration
In step 3 of the basic flow to calibrate the frequency and equation for the absolute error (ppm) is given as |10x6(Fmeasured - Frtcclk)/Frtcclk|. I am wondering if the denominator of this equation should not be Fmeasured instead of Frtcclk??? Each adjustment will be made with respect to the actual frequency (Fmeasured), not the desired frequency.
2) 23.2.5 In the NOTE: Minimum Possible Calibration
The actual text in the note is as follows:
"The minimal calibration possible is -4 ppm or +8 ppm. For example, setting RTCCALS = 0
and RTCCAL = 0h would result in a -4 ppm decrease in frequency. Similarly, setting
RTCCALS = 1 and RTCCAL = 0h would result in a +8 ppm increase in frequency."
This appears to be incorrect to me. If the RTCCAL value is 0h then I believe that the calibration feature is disabled and no frequency increase or decrease is made no matter what the value of RTCCALS is. Is this not correct???
In addition, I think the minimum possible correction should be:
+4.34ppm when RTCCALS = 1 and RTCCALx = 1
and
-2.17 when RTCCALS = 0 and RTCCALx = 1
Is this not correct??? If not, then the equations for calculating RTCCALx are even more wrong!
Thanks
Greg Dunn