STM32F103 and RS-485 on internal HSI?

[Astrid]

Is a good idea use STM32F103 only with internal HSI oscilator if this device communicate over RS-485 (38400bps) and work in temperature (-10 ~ +50 C)?

Datasheet say accuracy HSI is TA = –10 to 85 °C –1.5 - 2.2%.
HSI is User-trimmed with the RCC_CR register , but the trimming step is about 40kHz (0.5%/step) and thus do not even know whether it has any additional calibration sense.
I considered. Set MCO output on HSI , read frequencies on external Frequency counter and calibrate.
During the calibration step of 40kHz but it does not make sense to me or you're wrong?

Your opinion can operate RS-485 interface for communicating with an internal oscillator or crystal is required?

 

[tilz0R]

I don't know what is cause to use HSI, where external 8MHz crystal costs like 5 cents. It's quite high speed for your RS485 network.

 

[Astrid]

SMD, crystal 5mm x 3.2mm does not cost 5 cents, but this is not essential. I need inputs used for other purposes, and I do not want to use a larger case MCU