Frequency Calculation

Prior to issuing the trace command T, the Spock Sample Address Registers R3 and R4 should be programmed (usually with zero) and Spock initialized with the > command. When the trace is initiated, it starts counting input cycles immediately. The trigger logic is not used. When the programmed cycle count is reached, the trace stops and the frozen value of the 16 bit Sample Address Register returned.

The input signal frequency F may then be calculated as:

F = FS * CC / (SP + 2)

where:

FS	ADC sample clock rate (25 or 50 MHz).
CC	Pre-programmed frequency measurement cycle count.
SP	Measurement period (ie, sample address count).

In BitScope systems with a 25 MHz ADC clock, the maximum cycle count allows frequencies of up to 50 MHz to be measured.

If the clock doubler is installed the maximum measurable frequency is 100 MHz.