There are two ways in which the Low Level Alarm (LLA) system works on the 851S201I multiplexer:
- As an Amplitude Detection Circuit: Asserts the LLA indicator when the voltage on the differential clock inputs selected by CLK_SEL is less than 325 mV.
- As an Activity Detection Circuit: Asserts the LLA indicator when differential clock inputs selected by CLK_SEL stop switching (signals stuck at logic high, stuck at logic low, or they don't appear to switch because they are shorted together).
LLA only works on the selected input for both activity and amplitude detection. The LLA indicator only reflects status of the selected input.
For the activity detection to function, the other clock has to be present. The activity detection circuit portion of the low level alarm will only work when both CLK inputs are switching, and their frequencies are within 50% of one another.
The amplitude detection circuit portion of the LLA alarm will always work, regardless of frequency or whether or not both CLK inputs are switching.
The table below provides further clarification.
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