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ADS8556EVM,INT mode

dirk bonebrake
Prodigy 20 points
Other Parts Discussed in Thread: ADS8556

I'm using the ADS8556 EVM in parallel,software mode. Setting the CR to 0xE22007FF.

The goal is to keep the INT line high until all the conversions (all 6 channels) have been read.

When I look at the signals on a scope, the INT line goes high ~1.2 us after CONVST, and

goes low after a single reading (RD# low).

The datasheet (p 12) reference to the BUSY/INT line indicates that when C21=1 INT 'remains high

until the conversion result has been read'. I interpret this to mean that all channel data has been

read (6 words). As far as I can tell, I've got the board setup correctly to acquire all three ADC

pairs.

 

Am I doing something incorrectly, or misinterpreting the data sheet?

 

Also, is there an errata for the ADS8556, or an update to the data sheet? Shouldn't the

units for tCONV on p. 15 be us instead of ns? And the description of C20 in table 3 doesn't appear

correct; when the bit is 0 INT is active high.

 

Thank you

 

  • 0
    TI__Guru 55466 points

    Hi Dirk,

    I believe that the INT behaviour you are seeing is correct; but I will need to confirm with the design team. 

    I think the INT pin becomes high after the conversion is completed (1.2uS); and the INT is transitioning low after you read the data for one channel; although the datasheet seems to imply that the INT should transition low after the conversion result is read (six channels).  I will confirm with the design team if this is the device expected behaviour and clarify the explanation on the datasheet if this is correct.

    You are correct, the tCONV time should be microseconds; and the datasheet needs to be corrected.

    Thank you,

    Kind Regards,

    Luis Chioye

     

  • 0 in reply to Luis Chioye
    TI__Guru 55466 points

    Hi Dirk,

     

    I have verified with the design team the interrupt output function.  When the control register bit C21=1, and the device is used in parallel mode, the interrupt turns high when the conversion is completed, indicating the conversion data is available; and transitions low after the first falling edge of the RD signal.

     

    The datasheet will be updated with the correct explanation.  The device is working as expected.

     

    Thank you,

     

    Kind Regards,

     

    Luis

     

  • 0 in reply to Luis Chioye
    Prodigy 20 points

    Luis -

    Thank you for your prompt and clear resolution of this issue.

     

    I humbly suggest that when the datasheet is updated, a timing diagram for the INT behavior

    is included (as well as clarifying the signal description).

     

    Thank you

    D