Jim, I read the PAP section (7.3.18). There, it says "...if the data clock is lost, the FIFO would automatically generate a single tone signal..." Does "single tone" actually mean "single value" (i.e., DC)? If so, would the alarm condition depend on what value was being received when the stream stopped? For example, if it happened to stop while zero was being received, then would be no threshold that could be used to detect the condition. Note that we are using only real data at the JESD input. What is the signal labeled "Input" on the left side of figure 74? Is that coming from the output mux, so that the the mixer and other DSP would have been applied? I am considering a different mechanism, using the FIFO read error status. It is not ideal, and will require some experimentation, but it may work in a limited way. The disturbance that causes the DAC output to stop happens at a known time. Now that I understand how the FIFO read error alarm works I think I can use it to tell me that the disturbance may have caused the output to stop. Basically, the disturbance is in the sample clock (and SYSREF) when the receive channels (ADC) JESD is initialized. A common clock and SYSREF are shared for the ADC and DAC systems. The idea is that the DAC would be brought up and, if bringing up the ADC subsystem causes a FIFO read alarm, then I would assume that the DAC has stopped outputting. I know that only 1% of the time the DAC will actually not be outputting, but what I am hoping (and need to confirm) is that 100% of the time the DAC will be outputting if the FIFO alarm is not triggered. Lance
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