What is max LPUART baud rate of KL1x parts?

[paulferrari]

I calculate the max baud rate of the two LPUARTs on the KL16 and KL17 as 12Mbps.  Can someone confirm this?

According to Table 5-1 of the Reference Manual the LPUART0 clock rate is 48MHz in run mode.

Figure 35-3 (in the LPUART chapter)

shows the Baud Rate = (LPUART ASYNCH Module Clock) / (SBR(12:0) * (OSR+1))

I believe SBR(12:0) can be 1 and OSR can be 3.  This would result in 48MHz/(1*(3+1)) = 48MHz/4 = 12Mbps

I am fairly certain of this, but would appreciate a second set of eyes on this.

Thanks,

Paul

[Robin_Shen]

Hi Paul,

As you shared formula of LPUART baud rate generation, it can up to 12Mbps in RUN mode, and in VLPR mode, it is limited to 1Mbps.

So the LPUART can support to configure to up to 12Mbps, but actually, some conditions will impact its performance in really application, such as TX and RX loading(parasitism capacitance or inductance) on board, and the clock deviation and so on, and even result in communication fail, so need to take care of it.

I have test it on my FRDM-KL27Z board with lpuart driver example in the SDK_2.0_MKL27Z64xxx4.

Best Regards,

Robin

[schmikeee]

It's great to see this kind of speed capability in such a small part, but I also wonder if CPU loading from other basic processing tasks will limit the REAL baud rate?  In other words, if I tried running the 2 LPUARTs at 12Mbps, can the core do ANYTING else?

[chris_brown]

Hi Mike,

If you tried to use the core to service the LPUART, then there may be a bandwidth issue.  However, if you use the DMA, I would expect that the core would be freed up to perform other tasks. 

Regards,

Chris

[egoodii]

If you run them in DMA mode, there will be 'little' impact on core performance -- but of course the REAL question is what must firmware DO with all this traffic, and can THAT be 'short enough per byte' to keep up.

[chris_brown]

Hi Paul,

That is correct.  For these particular parts in the configuration you have mentioned, that is the maximum baud rate.  Take care to enable Both Edge Sampling (UART_C5[BOTHEDGE]) when using OSR values this low.  Also, remember that if you move to VLPR mode you should be limited to 1 Mbps. 

Regards,

Chris