Rev. 1.0
51
Si4010-C2
When the interval counter is finished with the interval count, it clears the FC_BUSY=0 bit and after a few
cycles of
clk_sys
synchronization delay it sets the FC_DONE=1 bit. Both interval counter and main
FC_COUNT counter are stopped and the main FC_COUNT keeps the accumulated value until the fre-
quency counter is disabled or triggered again. The 23 bit FC_COUNT value can be read as a 4 byte long
word,
lFcCount
, from the XREG register in XDATA. When the counter is counting and FC_BUSY=1, then
reading the FC_COUNT value returns the on the fly changing value of the FC_COUNT counter.
The frequency counter is restartable. If 1 is written to FC_BUSY while the frequency counter is busy then
the current FC_COUNT result is discarded, main FC_COUNT is reset, and the interval counter is trig-
gered, waiting for the first rising edge of the
clk_int
clock.
The count interval is chosen with the FC_INTERVAL SFR register. The number of interval count cycles
(count cycles of the low frequency clock) = (2+FC_INTERVAL[0])*(2^FC_INTERVAL[5:1]).
Note:
FC_INTERVAL is not allowed to take on numbers higher than 43. If the number is higher than 43, then the
calculated number or interval count cycles is forced to 1. Even though 43 is the maximum FC_INTERVAL
setting, lower FC_INTERVAL settings can cause the 23-bit frequency counter to overflow depending on the
ratio between the frequency counter clock and the interval clock. Generally, the ratio between these clocks
should be carefully selected to prevent overflow of the frequency counter (unless overflow is explicitly desired).
The output of the frequency counter is in the XREG FC_COUNT.
The main function of the Frequency counter is to aid the frequency casting operation, however it can be
used for measuring purposes, using the calibrated LC oscillator as a time base. One example is enhancing
the accuracy of the internal timers of the MCU. See “AN526: Si4010 API Additional Library Description” for
more details.
The user is recommended to use the Frequency Counter Module Function API to set the SFRs associated
to the Frequency Counter.
