Autonomous Clock Trimming Register Details needed for MC9S12ZVC micro

[anwarhusengokav]

Hi Radek,

I would like to configure the Autonomous Periodical Interrupt to wakeup the MCU every 10sec. Could you please provide me the details about the significance of the Autonomous Clock Trimming Register? PFA the attached details from the reference manual. 

For your information, I have configured as follows:

CPMUACLKTR = (CPMUACLKTR_ACLKTR1_MASK|CPMUACLKTR_ACLKTR2_MASK|CPMUACLKTR_ACLKTR4_MASK);

Clock source for API is ACLK

CPMUAPIRH = 0xD7u;
CPMUAPIRL = 0x40u;

I observe a drift of around 200ms. And it is varying board to board. What could be the reason?

Thanks in advance. 

Wish you a wonderful Happy New year 2017.

With Best Regards,

Anwar

[RadekS]

Hi Anwar,

The ACLK is a signal from internal RC oscillator.

The frequency of ACLK varying MCU to MCU. Therefore, every MCU should be trimmed for achieving the target +/-6% deviation from 20kHz (specified only for trimmed ACLK signal).

Since you modified CPMUACLKTR value and set the same value for all MCUs, you effectively disable factory trimming of ACLK signal and result API timeout will vary between boards per their ACLK signals.

I would like to recommend use factory trimming (do not modify CPMUACLKTR register value). The trimming value from the factory is automatically loaded from flash IFR field to CPMUACLKTR register during reset sequence. The exception may be only first engineering MCU samples which do not have full trimming yet.

If you are not satisfied with factory trimming (e.g. when you need 22kHz), you may do your own trimming and modify CPMUACLKTR register value after every reset. However, this trimming must be made at every single MCU separately.

I hope it helps you.

Have a great day,
Radek

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