SPRUID8D September 2020 – January 2022 TMS320F280040-Q1 , TMS320F280040C-Q1 , TMS320F280041 , TMS320F280041-Q1 , TMS320F280041C , TMS320F280041C-Q1 , TMS320F280045 , TMS320F280048-Q1 , TMS320F280048C-Q1 , TMS320F280049 , TMS320F280049-Q1 , TMS320F280049C , TMS320F280049C-Q1
The calibration logic consists of two free-running counters; one clocked by HRCLK(HRCLKCTR) and the other clocked by SYSCLK(HRSYSCLKCTR). When HRSYSCLKCTR is equal to HRCALIBPERIOD, the calibration block will capture and reset both counter values, then trigger an interrupt indicating a new scale factor is ready to be calculated. The scale factor can be found by dividing HRSYSCLKCAP by HRCLKCAP, see Equation 1. This scale factor computation should be done inside of the calibration interrupt service routine. After computing scale factor, Equation 2 can be applied to get actual measurement of captured value from raw count.
The full details of the calibration block are described in Figure 6-6.
Even with calibration, noise on the 1.2 V VDD supply will negatively affect the standard deviation of the HRCAP sub-module. Care should be taken to ensure that the 1.2 V supply is clean, and that noisy internal events such as enabling and disabling clock trees have been minimized while using the HRCAP.