S32KのトピックRe: Max baudrate LPUART2 for FS32K144

Max baudrate LPUART2 for FS32K144

bryan_hong — Wed, 16 Aug 2023 10:14:19 GMT

How much maximum LPUART2 Baudrate can be set for stable communication on FS32K144

danielmartynek — Thu, 17 Aug 2023 07:56:01 GMT

The LPUART functional clock can be set up to the BUS_CLK freq, which is 56MHz in HSRUN and 48MHz in RUN.

Baudrate = LPUART functional clock / SBR (min 1) * OSR (min 4)

danielmartynek_0-1692193302149.png

danielmartynek_1-1692193332539.png

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That means the baudrate can be even 14 MHz in HSRUN.

This is rather limited by the AC electrical specification of the IOs and by the electrical characteristics of the bus.

S32K1xx, Datasheet, rev14

5.1 AC electrical characteristics

5.2 General AC specifications

Table 23. AC electrical specifications at 5 V Range for S32K1xx series

Regards,

Daniel

bryan_hong — Thu, 17 Aug 2023 00:17:15 GMT

thanks Daniel for quick updates.

How to get the 14Mhz ?

48/1*(4+1) = 9.6

danielmartynek — Thu, 17 Aug 2023 07:55:25 GMT

Theoretically in HSRUN.

56 MHz / (1 * (3 + 1)) = 14 MHz

BR, Daniel

bryan_hong — Thu, 17 Aug 2023 08:20:24 GMT

thanks for update

Not theoretically, can this be enabled stable in practice?

Is there a use case for max baudrate that was actually used?

Bryan

danielmartynek — Thu, 17 Aug 2023 09:16:40 GMT

Why do you need this baudrate? I'm not aware of such a use case.

With this configuration, there would be oversampling rates of 4x.

danielmartynek_0-1692263064869.png

The baudrate (14 MHz) would have 71.4ns period.

There are no GPIO-HD (PORTn_PCR[DSE] = 1) LPUART pins, only GPIO (PORTn_PCR[DSE] = 0), refer to S32K144_IO_Signal_Description_Input_Multiplexing.xlsx

At 200pF bus capacitance, the slew rate of the pins can be up to 54.8ns / 5V (Rise time), 59.7ns / 5V (Fall time).

danielmartynek_1-1692263651197.png

As you can see, it depends on the electrical characteristics of the bus.

Regards,

Daniel