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ADC081S021: Affect of sample abort on throughput?

Part Number: ADC081S021
Other Parts Discussed in Thread: ADS7040

The datasheet states that the sample is aborted "if CS is brought high after the 10th falling edge, but before the 16th falling edge," however the implications of this on the timing of the next /CS falling edge are not addressed.  On what edge is an abort recognized, and does the device immediately return to Track mode when this happens, or is it expected that clocking continues and that Track mode is still entered normally after 12.5 clocks?

Put another way, is the minimum time between falling edges of /CS at all impacted at all by an abort, provided clocking continues?

For the curious, this is not a performance optimization question.  Rather, I'm constructing some minimalist logic to read out a serial ADC and would like the result to be compatible with as many inexpensive 8-bit ADCs as possible (other likely candidates being the ADS7029 and ADS7040).  The 16-cycle 1-MHz scenario described in the Throughput section is quite attractive for my purpose, however due to the extreme scarcity of hardware resources, the exact duration of /CS requires some careful budgeting.  My hope would be that the 16-cycle 1-MHz frame timing holds, regardless of whether the sample is "aborted" immediately after DB7 is output.  

Very best,
Aaron

  • Hello Aaron, 

    Looking at the timing diagrams in the datasheet, one may be able to collect this data

    CS has to have a minimum high pulse of 10ns. When CS is brought high the SDATA is instantaneously set to tri-state. Note, this can be in parallel to the Tquiet time of 350n, but both these requirements are independent and both must be met for the next conversion. 

    The acquisition time is set specifically by the SCLK, not CS, and from the timing diagram, if CS if high the SCLK are still valid, even if SDATA is in tri-state. thus one can infer that acquisition phase will not start, if aborted, until the clock pulse requirement is met 

  • Hi, Cynthia - Thank you.  The Throughput section describes a 16-cycle frame at 1MHz.  The specific timing of the rising edge of /CS is not a part of the formulation at all, however because the word "abort" is not mentioned, one might assume that the rising edge occurs after the 16th falling edge of SCLK, and therefore that the /CS pulse width must be less than half an SCLK cycle.  Since half an SCLK at 1MHz is 500ns, which is larger than both Tquiet and Tacq, it can work.  If raising /CS prior to the 16th falling edge of SCLK, while continuing clocking, simply tri-states SDATA before it would normally go tri-state on its own, then everything would still work, and /CS could be raised at any point after all actual data bits are output without breaking the 16-cycle frame timing.  I'd like to *think* this is the case, however the datasheet just isn't explicit about what abort actually means.  If one aborts and does not keep clocking while idle, the behavior would seem to be even less clear, although that's not a scenario that's relevant to me.

  • Aaron,

    I agree with your assessment. This device was  released is 2005, there have been improvements in the documentation of our devices since then. 

    Another option is to use the EVM ~click here~ to test this scenario

    Regards

    Cynthia