SPRUHX5I August 2014 – May 2024 TMS320F28374S , TMS320F28375S , TMS320F28375S-Q1 , TMS320F28376S , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28378S , TMS320F28379S
The ramp generator produces a falling ramp input for the high-reference 12-bit DAC when selected. In this mode, the reference 12-bit DAC uses the most-significant 12 bits of the RAMPSTS countdown register as the input. The low 4 bits of the RAMPSTS countdown register effectively act as a prescale for the falling ramp rate configurable with RAMPDECVALA.
The ramp generator is enabled by setting DACSOURCE = 1. When DACSOURCE = 1 is selected, the value of RAMPSTS is loaded from RAMPMAXREFS and the register remains static until the selected EPWMSYNCPER signal is received. After receiving the selected EPWMSYNCPER signal, the value of RAMPDECVALA is subtracted from RAMPSTS on every subsequent SYSCLK cycle.
To prevent the subtraction from commencing a SYSCLK cycle after a EPWMSYNCPER event, the RAMPDLYA register that serves as a delay counter can be used to hold off the RAMPSTS subtraction. On receiving a EPWMSYNCPER event, the value of RAMPDLYA is decremented by one on every SYSCLK cycle until the register reaches zero. So, the RAMPSTS subtraction only begins when RAMPDLYA is zero.