SPRUHM8K December 2013 – May 2024 TMS320F28374D , TMS320F28375D , TMS320F28376D , TMS320F28377D , TMS320F28377D-EP , TMS320F28377D-Q1 , TMS320F28378D , TMS320F28379D , TMS320F28379D-Q1
There are two settings to configure for each PLL – a multiplier and a divider. They obey the formulas:
fPLLSYSCLK = fOSCCLK * (SYSPLLMULT.IMULT + SYSPLLMULT.FMULT) / SYSCLKDIVSEL.PLLSYSCLKDIV
fAUXPLLCLK = fAUXOSCCLK * (AUXPLLMULT.IMULT + AUXPLLMULT.FMULT) / AUXCLKDIVSEL.AUXPLLDIV
where fOSCCLK is the system oscillator clock frequency, fAUXOSCCLK is the auxiliary oscillator clock frequency, IMULT and FMULT are the integral and fractional parts of the multipliers, PLLSYSCLKDIV is the system clock divider, and AUXPLLDIV is the auxiliary clock divider. For the permissible values of the multipliers and dividers, see the documentation for their respective registers.
Many combinations of multiplier and divider can produce the same output frequency. However, the product of the reference clock frequency and the multiplier (known as the VCO frequency) must be in the range specified in the data sheet.
The system clock frequency (PLLSYSCLK) may not exceed the limit specified in the datasheet. This limit does not allow for oscillator tolerance.
The clock source and PLL configuration registers are shared between the two CPUs. Register access is controlled via a semaphore, which is described in the Inter-Processor Communication chapter.