How to read 18-Bit SPI with MPC5744P ?

[Pat]

Hi all,

I have 4x AD7608 from Analog Devices connected on the same SPI bus. The AD7608 is a simultaneous 8-channel with 18-Bit simultaneous sampling ADC.

The MPC5744P has the frame Size (FMSZ) limited to 16-Bit in Master mode.

Therefore the only way to achieve the read of 18-bit data is to emulate the SPI by DMA ?

Best regards,

Pat

[PetrS · Accepted solution]

Hi,

You should be able to set the SPI module for 9bit data transfer and send 2 words with Continuous selection format. That is set the CONT bit in the first SPI command and clear it in second one (last one).

  See more in the DSPI chapter of the device Reference manual.

BR, Petr

[Pat]

Hi Petr,

Thank you.

I would like to use the DMA with SPI in order to retrieve the 32 samples (8-channels *  4-ExternalAdcChips).

In this confguration, the RxFIFO will count 2 entries ?

Do you have a demo example with SPI-DMA ?

Best regards,

Pat