Datasheet

151

7734Q–AVR–02/12

AT90PWM81/161

13.5 Functional Description

13.5.1 Waveform Cycles

The waveform generated by PSCR can be described as a sequence of two waveforms.

The first waveform is relative to PSCOUTr0 output and part A of PSC. The part of this waveform

is sub-cycle A in Figure 13-3.

The second waveform is relative to PSCOUTr1 output and part B of PSC. The part of this wave-

form is sub-cycle B in Figure 13-3.

The complete waveform is ended with the end of sub-cycle B. It means at the end of waveform

Figure 13-3. Cycle presentation in 1, 2, and 4 Ramp mode.

Ramps illustrate the output of the PSCR counter included in the waveform generators. Centered

Mode is like a one ramp mode which count down up and down.

Notice that the update of a new set of values is done regardless of ramp Mode at the top of the

last ramp.

13.5.2 Running Mode Description

Waveforms and length of output signals are determined by Time Parameters (DT0, OT0, DT1,

OT1) and by the running mode. Three modes are possible:

– Four Ramp mode

–Two Ramp mode

–One Ramp mode

The active time of PSCOUTn0 is given by the OT0 value. The active time of PSCOUTn1 is given

by the OT1 value. Both of them are 12 bit values. Thanks to DT0 & DT1 to adjust the dead time

between PSCOUTn0 and PSCOUTn1 active signals.

4 Ramp Mode

2 Ramp Mode

1 Ramp Mode

Sub-Cycle ASub-Cycle B

PSC Cycle

UPDATE

Ramp A0 Ramp A1 Ramp B0 Ramp B1

Ramp A Ramp B