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connecting 2 converters to OMAPL138 through SPI

Rachel Coulter
Intellectual 880 points
Other Parts Discussed in Thread: OMAPL138, DAC7654

Hello I have questions about connecting converters to the OMAPL138. I'm not sure if this is the right forum, and if not please let me know where to post or who to talk to.

1)      Can two devices (DAC and ADC) be connected to SPI0 (off of the OMAPL138) and still meet timing requirements? Also do you have any app notes on connecting a SPI DAC and ADC off the same port?

2)      We are currently connecting the eval board DAC7654 to the OMAP ref board.  Do I need to connect the LOAD and LDAC lines to a GPIO on the OMAP?  Or can the DAC function without these two lines? 

 

Thanks,

Rachel

  • TI__Intellectual 880 points

    I was able to answer my own question :)

    1)      Can these two devices (DAC and ADC) be connected to SPI0 and still meet our timing requirements?

     No app notes however set up should be fairly simple. Basically they can both be connected however you will need 2 separate chip select lines, one going to the DAC and the other going to the ADC. Then the clock and data lines can go to both and the timing requirements will not be affected. You won’t be able to simultaneously talk to both however and the chip select line will control which converter you are talking too. 

    2)      We are currently connecting the eval board DAC7654 to the OMAP ref board.  Do I need to connect the LOAD and LDAC lines to a GPIO on the OMAP?  Or can the DAC function without these two lines? 

     For the DAC7654, you do need both of these lines. The LOAD controls the input register and needs to be held low (to make it transparent)

    The LDAC pin controls the DAC register and needs to be free to pulse. This controls when to update and it is edge triggered so needs to able to see that rising edge to update.