topic Re: LPUART0 baudrate in Kinetis Microcontrollers

LPUART0 baudrate

akimata — Fri, 27 Jul 2018 10:05:23 GMT

Hello,

I've got problem with setting baudrate highter than 9600.

Microcontroller : K82

Clock is internal fast oscillator 4MHz

According to this :

Baud Rate = LPUART ASYNCH Module Clock / (SBR[12:0] × (OSR+1))

If i set SBR at 13, and OSR at 31 i get almost 9600 and it works just fine but the problem starts when i want any higher baudrate, let's say i will set SBR at 3 and OSR at 31 and i should get something close to 41500 according to the formula but according to oscilloscope i get something close to 18000. It gets even worse when LPUART0 source is FLL.

Is there any script or software to get as close to standard baudrates or i need to find right numbers(dividers) by myself?

What am i missing? Where's the catch?

Re: LPUART0 baudrate

miduo — Mon, 30 Jul 2018 08:32:51 GMT

Hi,

Please make reference from this post on how to config the baudrate. Although it is for K22, but the proceduce for K82 is same. https://community.nxp.com/message/669194

https://community.nxp.com/message/1012371

Re: LPUART0 baudrate

akimata — Mon, 30 Jul 2018 09:57:16 GMT

I read almost every post about lpuart, config is correct except baudrate and clocking.

Baudrate clock/(SBR*(OSR+1))

How is 4MHz/(13*(31+1)) = 9615 not equal to: 4Mhz/(26*(15+1) )= 9615, in theory they're equal but both settings gives me 2 different baudrates so it looks like there is strange corelation between OSR and SBR.

@Edit

I noticed that only 16 and 32 can be set in OSR (15 and 31), any other value results in getting 16/32. In SBR field there is always "1" on third spot from LSB, so if i set 8 result in 12, value of 12 results in 12 etc.

Also there is no way to set FLL/PPL or IRC48M in SIM_SOPT2, value in the register doesn't want to change or clear, only fast internal oscillator can be set.

Knowing these problems i could easily set specific baudrate but achieving 57200 or any higher baud is just impossible when i can't manipulate OSR and SBR freely.

Noticed that on custom K80 board also on FRDM-K82.

Any ideas what might be wrong?