STM32H7 Max UART Baudrate

[Holger Sachs]

Posted on November 24, 2017 at 16:15

I tried to figure out the specification of the max. UART baudrate for the SM32H7 series (@ 400MHz system clock).

The data sheet says 12.5 MBit.

Does this apply to all UART ports or only selected ones?

I need 8 MBits @ 16x oversampling and 6 MBits @ 8x oversampling.

Are these baudrates possible?

Best regards,

Holger

[Uwe Bonnes]

Posted on November 24, 2017 at 17:33

RM0433 table 51 states the maximum  peripheral clock. For all U(S)ART it is 100 MHz. That means 12.5 MBaud @ 8 oversampling and 6.25 at 16 oversampling. 8 x 16 in your question above needs 128 MHz peripheral clock, beyond the specs. Maybe overclocking the uart peripheral clock can be an option, if you dare.

B.t.w, I miss the spec for the maximum  peripheral clock frequency  in the datasheet and in Stcube!

[Tesla DeLorean]

Posted on November 24, 2017 at 18:00

The choice of dividers in the STM32 designs tends to work against you, especially at higher/maximal rates. These rates are also rather high for async comms, sure you can't use a better protocol or something synchronous? The STM32 USART designs also lack any FIFO, you might be better considering and external part optimized for such rates and attached to the FSMC

[Uwe Bonnes]

Posted on November 24, 2017 at 21:38

Ths STM33H7 Usart _has_ a FIFO

[Tesla DeLorean]

Posted on November 24, 2017 at 22:42

Ok, yes seems to have 16 word RX and TX.

[Harvey Zhang]

You can use up to 125MHz clock source to USART peripherals on H7 if you use CubeMX to configure the clock tree. Then the baudrate can be up to 125/8 or 125/16 depending on the oversampling configurations. But ST HAL driver will stop you from using baudrate higher then 12.5M if assert_param is enabled.