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SPI Minimum clock speed

Prad1
Genius 3825 points
Other Parts Discussed in Thread: AM1808, AM1705

Hi,

Our system has an external ADC connected through SPI at 200KHz.
We would like to know if AM1705 or AM1808 as a Master supports SPI communication at that low speed?
The AM1705's datasheet mention's SPI clock Cycle Time as "greater of 3P or 20(MIN) and 256P(MAX)".
But we couln't understand if there is an option to set SPI clock to 200KHz
and in that case will it cause any side effect on the clock speed of other peripherals?

Regards.
Prad

  • 0
    Guru 26430 points

    SPIs are clocked by SYSCLK2 which is usually half of the processor clock. If the processor clock is 375MHz then SYSCLK2 is 187.5MHz. The SPI module supports a maximum prescaler of 256. The SPI clock can be divided down to 187.5/256 = 732.4kHZ. In theory SYSCLK2 could be divided down more to get a lower SPI clock but SYSCLK2 is used by PRU, UARTs, EDMA, SPIs, MMC/SD, Shared RAM, eCAPs, eQEPs, eHRPWMs, McASPs, USB2.0, ARM RAM/ROM and EMIFB. See spruh93b.pdf.

    Maybe use use GPIOs and bit-bang the SPI signals?