143
4317I–AVR–01/08
AT90PWM2/3/2B/3B
16.7.2
Modes of Operation
16.7.2.1
Normal Mode
The simplest mode of operation is the normal mode. See
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 ajust the dead time
between PSCOUTn0 and PSCOUTn1 active signals.
The waveform frequency is defined by the following equation:
16.7.2.2
Enhanced Mode
The Enhanced Mode uses the previously described method to generate a high resolution
frequency.
Figure 16-13. Enhanced Mode, Timing Diagram
The supplementary step in counting to generate f
b2
is added on the PSCn0 signal while needed
in the frame according to the fractional divider. See
Table 16-5, “Distribution of fb2 in the modu-
.
The waveform frequency is defined by the following equations:
d is the fractionel divider factor.
f
PSCn
1
PSCnCycle
------------------------------
=
f
CLK_PSCn
OT
0
OT
1
DT
0
DT
1
+
+
+
(
)
----------------------------------------------------------------------
1
=
=
=
PSCOUTn0
T1
Period
PSCOUTn1
OT0
OT1
DT1
DT0
T2
OT0
OT1+1
DT1
DT0
DT0
f
1
PSCn
1
T
1
------
f
CLK_PSCn
OT
0
OT
1
DT
0
DT
1
+
+
+
(
)
----------------------------------------------------------------------
=
=
f
2
PSCn
1
T
2
------
f
CLK_PSCn
OT
0
OT
1
DT
0
DT
1
1
+
+
+
+
(
)
--------------------------------------------------------------------------------
=
=
f
AVER AGE
d
16
------
f
1
P SCn
×
16
d
–
16
---------------
f
2
PSCn
×
+
=
