SLAZ279AA October   2012  – May 2021 MSP430F5418

 

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6.84 RTC6

RTC Module

Category

Functional

Function

the step size of the RTC frequency adjustment is twice the specified size.

Description

In BCD mode of operation, the step size of the RTC frequency adjustment is =+12ppm/-4ppm. This is thrice the size specified in the User's Guide for up-calibration and twice the size for down-calibratin.
In Binary mode of operation, the step size of the RTC frequency adjustment is =+6ppm/-2ppm. This is 1.5x the step size specified in the User's Guide for up-calibration and is as per spec for down-calibration.

In BCD mode, for up calibration this results in a step size per step of 12ppm (1536 cycles) instead of 4ppm (512 cycles). For down calibration this results in a step size per step of 4ppm (512 cycles) instead of 2ppm (256 cycles).
In Binary mode, for up calibration this results in a step size per step of 6ppm (768 cycles) instead of 4ppm (512 cycles). For down calibration this results in a step size per step of 2ppm (256 cycles) as in spec.

Workaround

To compensate for the erratic step size, the RTCCAL register can be written with
1/3 of the calibration value for BCD up mode, 1/2 of the calibration value for BCD down mode and 1/1.5 of the calibration value for Binary up mode.