Kinetis Microcontrollers中的主题 Re: Last ISR Vector in MEK18 Startup s file

Last ISR Vector in MEK18 Startup s file

sean_dvorscak — Wed, 30 Nov 2022 23:08:05 GMT

I was looking through the startup_MKE18F16.s file, and had a question about what the 255th entry in the vector table.

The last entry shows a value of: DCD 0xFFFFFFFF ; Reserved for user TRIM value

I cannot find any information on what this TRIM value is. Can someone either tell me what this is or point me to some documentation for this?

Re: Last ISR Vector in MEK18 Startup s file

Miguel04 — Thu, 08 Dec 2022 18:17:42 GMT

Hi @sean_dvorscak

A trim value is a reference value stored in the non-volatile memory which is used by the mcu to initialize and calibrate (in this case) the clock once it occurs a power-cycle, this values allow the frequency to be almost constant during the mcu operation. This post could give you a better idea of what trimming is.

Let me know if you have another question.

Best Regards, Miguel.

Re: Last ISR Vector in MEK18 Startup s file

sean_dvorscak — Thu, 08 Dec 2022 18:43:58 GMT

Hi @Miguel04

So this is the trim value for the internal oscillator? Is that part of the "High Range OSC" shown in figure 18-1 of the reference manual?

Would like to know more about what clock(s) exactly are affected by this and how exactly the trim value configures the clock? Something like a formula.

Thanks for the help.

Re: Last ISR Vector in MEK18 Startup s file

Miguel04 — Tue, 20 Dec 2022 16:38:13 GMT

Hi @sean_dvorscak

I've been looking for the information.

Every main clock of the SCG needs to be trimmed, and there isn't a specific formula for the clock to be trimmed, instead there is a register (for example SCG_FIRCSTAT) which coursely trim the Fast IRC Clock to within approximately ±0.7% of the target
frequency. Chapter 19.3.18 reference manual.

Sorry for the late reply, let me know if you have another question.

Best Regards, Miguel.