SCPS286 July 2025 TPLD2001
ADVANCE INFORMATION
When configured as a Frequency comparator (FCMP), this macro-cell will indicate whether the input signal is faster or slower than the period specified by DATA. The initial output value of this macro-cell after device startup can also be configured to Bypass Initial, Initial Low, or Initial High. The edge on which the Frequency comparator is reset is determined by the Edge select parameter and can be configured as:
Rising: rising edges of IN trigger and reset the frequency comparator.
Falling: falling edges of IN trigger and reset the frequency comparator.
Both: rising edges of IN triggers the frequency comparator to begin counting and falling edges of IN reset the frequency comparator.
Upon receiving a trigger, an additional 2 clock cycles is used to synchronize IN and the counter with CLK, then the counter begins decrementing from DATA on the following rising edge of CLK.
If the internal counter reaches 0, the FCMP macro-cell will output a Low signal, indicating the input frequency is slower than DATA. Otherwise, if the counter is interrupted with a reset before reaching 0, the FCMP macro-cell will output a High signal, indicating a faster signal on IN.
Figure 7-19 shows an example of how the FCMP macro-cell operates with respect to the Edge select parameter.