5.3.2.5 High Resolution Capture Mode
In high-resolution capture mode, the application code utilizes the HCCal HRCAP calibration library functions to
capture the high-resolution pulse width with each edge captured at a typical resolution of +/- 300 ps (with two
edges, the resolution of the measured pulse width could vary by +/- 600 ps). Note that although the HRCAP logic
itself can be calibrated to capture high-resolution pulse widths, if the jitter on the input signal is greater than +/-
300 ps, the captured value will also vary according to the jitter on the input signal.
In order to use high-resolution capture mode, the high-resolution capture logic must be calibrated to scale the
HRCAP step size to a Q16 fraction of the HCCAPCLK. One HRCAP module and the ePWM module internally
connected to the HRCAP calibration input must be dedicated only to calibration and cannot be used functionally
in the application during calibration.
Texas Instruments provides a calibration function in the HCCal HRCAP calibration library to perform this
calibration once prior to using the HRCAP in high-resolution capture mode and periodically in a slow loop to
account for changes in the HRCAP step size due to voltage and temperature changes while the application is
running.
The library also provides functions to measure the high resolution high pulse width, low pulse width, and period.
The pulse and period width measurement results are returned in Q16 fixed-point format with the fractional
portion of the result representing a fraction of an HCCAPCLK cycle. (For instance a pulse width may appear in
the form of 500.25 HCCAPCLK cycles).
shows how the high-resolution pulse width is a function of the
calibration of the HRCAP step size and the values in the HCCAPCNT registers.
HRCAPx
HRCAP step
~ 300 ps
HCCAPCLK cycle
8.33 ns at 120 MHz
Fn(HCCAPCNT registers, HCCal calibration)
0.0 – 0. in Q16 format
9
0.0 – 0. in Q16 format
9
Figure 5-8. HRCAP High-Resolution Mode Operating Logic
For details on using the HCCal HRCAP calibration library in high-resolution capture mode, see
High-Resolution Capture (HRCAP) Module
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
411
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Содержание TMS320 2806 Series
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