10% timing error using rtc

Jayesh Parmar

Other Parts Discussed in Thread: MSP430F5438A

Hi. I have an application in which the uc will generate an interrupt after 3 weeks. Im using MSP430f5438a for this. For testing i have set 3 days for interrupt but it generates the interrupt before 7 hours then the set time. What im doing wrong?

over 9 years ago

0 Clemens Ladisch over 9 years ago

Guru 316940 points

You are probably using REFO instead of XT1.

0 Chester Gillon over 9 years ago

Guru 92251 points

The title of the thread suggest that the RTC_A module in the MSP430F5438A is being used to generate the interrupt.

The "normal" use case for the RTC_A module is to have ACLK sourced from a 32768 Hz crystal connected to XT1 in LF mode, and the RTC_A module clock source to be ACLK.

If ACLK is being sourced from XT1 in LF mode and an oscillator fault occurs, ACLK is automatically switched to the REFO for its clock source. The REFO absolute tolerance calibrated over the full temperature range is ±3.5%. i.e. even if REFO was used as the clock source for ACLK and the RTC_C, that doesn't explain the observed 10% timing error.

Can you clarify how the interrupt is being generated, and the clock source for the timer which generates the interrupt.

0 Jayesh Parmar over 9 years ago in reply to Clemens Ladisch

Prodigy 215 points

Hi Clemens , Can you please elaborate on that?

0 Clemens Ladisch over 9 years ago in reply to Jayesh Parmar

Guru 316940 points

Chester already has explained this. But it is impossible to be more specific without seeing your code.

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10% timing error using rtc