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What is the maximum UART speed on the STM32H7B0xB?

Associate III

I'm looking at the STM32H7B0xB. I'm confused about what the actual maximum baud rate of the UART (in asynchronous mode) is. I'm getting three conflicting answers:

  1. Section 3.38 (the USART section of the datasheet) says: "These interfaces provide asynchronous communication, IrDA SIR ENDEC support, multiprocessor communication mode, single-wire half-duplex communication mode and have LIN Master/Slave capability. They provide hardware management of the CTS and RTS signals, and RS485 Driver Enable. They are able to communicate at speeds of up to 10Mbit/s.
  2. Section (the USART section of the datasheet "Electrical Characteristics") says that fck "USART clock frequency" in master mode is 35 MHz.
  3. When I use CubeMX to configure the UART, the highest UART speed I can get is 17.5 MHz (for asynchronous mode), and 10 MHz for synchronous mode.

Does anyone know what the maximum UART speed in asynchronous mode is for these devices?


General rule of thumb is the APB clock for the bus the U(S)ART is on DIV8, the H7B0 APB1/APB2 max speed is 140 MHz, so 17.5 Mbaud, but the rates will need to divide relatively cleanly so the rate error can get high (actual vs desired). And Asynchronous Serial isn't known for its robustness.

You can route in a usart_ker_ck through the kernel clock distribution tree. Need to find a table of maximum clocks there. Ok, so per RM fuart_ker_ck / fusart_ker_ck is 280 MHz, so 35 Mbaud

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