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AM3352: 800kbps CAN baudrate incompatible with 25MHz oscillator

DJ-NG
Genius 9355 points
Part Number: AM3352

Hi champs,

customer found, that with 25MHz external oscillator, they cannot achieve CAN baudrate 800 kbps, which is essential for them.

They found in documentation

http://www.phytec.de/documents/l-818e-4-am335x-bsp-manual/

that for 800KBd a 24 MHz oscillator must be used. This would mean reassembling and a new layout (boot pin changes).

Q: Can pls check, if 800 Kbps definitely need a 24MHz oscillator or can be achieved with 25MHz ?

  • 0
    TI__Guru**** 393215 points
    Hi,

    According to section 23.3.16.2.1 of the AM335x TRM Rev.P:

    "Usually, the calculation of the bit timing configuration starts with a desired bit rate or bit time. The resulting bit time (1 / Bit rate) must be an integer multiple of the CAN clock period."

    Since the CAN functional clock is derived from CLK_M_OSC, this calculation will give:

    (1/800000)/(1/25000000) = 31.25 which is not an integer
    (1/800000)/(1/24000000) = 30 which is an integer value