136
4317I–AVR–01/08
AT90PWM2/3/2B/3B
16.5.2
Running Mode Description
Waveforms and length of output signals are determined by Time Parameters (DT0, OT0, DT1,
OT1) and by the running mode. Four modes are possible :
–
Four Ramp mode
–
Two Ramp mode
–
One Ramp mode
–
Center Aligned mode
16.5.2.1
Four Ramp Mode
In Four Ramp mode, each time in a cycle has its own definition
Figure 16-6. PSCn0 & PSCn1 Basic Waveforms in Four Ramp mode
The input clock of PSC is given by CLKPSC.
PSCOUTn0 and PSCOUTn1 signals are defined by On-Time 0, Dead-Time 0, On-Time 1 and
Dead-Time 1 values with :
On-Time 0 = OCRnRAH/L * 1/Fclkpsc
On-Time 1 = OCRnRBH/L * 1/Fclkpsc
Dead-Time 0 = (OCRnSAH/L + 2) * 1/Fclkpsc
Dead-Time 1 = (OCRnSBH/L + 2) * 1/Fclkpsc
Note:
Minimal value for Dead-Time 0 and Dead-Time 1 = 2 * 1/Fclkpsc
16.5.2.2
Two Ramp Mode
In Two Ramp mode, the whole cycle is divided in two moments
One moment for PSCn0 description with OT0 which gives the time of the whole moment
One moment for PSCn1 description with OT1 which gives the time of the whole moment
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
Dead-Time 1
Dead-Time 0
PSC Cycle
OCRnRB
OCRnSB
OCRnRA
OCRnSA
PSC Counter
0
0
