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STM32F100RD, IrDA pulse width is 1.5uS, not 1.6uS, on 8MHz system clock

Question asked by yang.wenbo on May 8, 2014
Latest reply on May 8, 2014 by yang.wenbo
This is what I measured on scope when the STM32F100RD is working on 8MHz system clock, I tried to configure the system clock on 8MHz HSI, or to a 8MHz clock divided from 16Mhz HSE by set RCC_SYSCLK_Div2, the baud rate is 115.9Khz, but the IrDA pulse width is not exactly 3/16 or 1.63uS, instead, it's 1.5uS.

When I set the system clock to 16Mhz HSE, the pulse width is 1.68uS.

Since my application will be running on 8Mhz, I want to understand why the pulse width is shorter than the expected value from the spec.
 
I also attached my register bank for IrDA port here.

Thanks

PulseWidthOn8MHzSysClk.jpg

BaudRateOn8MHzSysClk.jpgIrDARegisterBank.jpg

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