at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 111

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

13.7.1
7734M–AVR–03/10
Frequency distribution
According to the ramp mode and the enhanced resolution mode (defined by PBFMn1:0), the average fre-
quency deviation Δf can take three different values:
These values are applied according to the running mode and the enhanced resolution mode as per
13-5 on page
It must be noted that, in one and two ramps modes, it is possible to apply the FWM only on pulse width
while keeping a constant frequency.
Table 13-5.
1.
The frequency modulation is done by switching two frequencies in a 16 consecutive cycle frame. These
two frequencies are f
is the nearest base frequency below the wanted frequency. The number of f
number of f
pattern. This pattern can be as given in the following table or by any other implementation which give an
equivalent evenly distribution.
At the end of the 15th cycle (numbered 14 on
the bit PEOEPEn (PSC n End Of Enhanced Cycle Interrupt Enable) is set. This allows:
Four Ramps
Two Ramps
One Ramp
Center aligned
• To modify the modulation only on a new enhanced cycle start.
• To extend the enhanced modulation accuracy by software.
Running Mode
Note: The modulation is on the pulse width.
b2
111;
is d. The f
Frequency deviation with Flank Width Modulation
b1
and f
b1
and f
b2
where f
b2
frequencies are evenly distributed in the frame according to a predefined
Δf1
Δf1
Δf1
Δf2
Δf1 average
RB
00
Δf2 average
b1
(
(
is the nearest base frequency above the wanted frequency and f
Δf average
Table 13-6
(
)
)
=
=
f
RB+RA
f
PSC
PSC
Δf2
Δf2
Δf1
Δf2
)
01
) an interrupt can be generated. This is the case if
=
×
×
------------------------- -
16k k
0
---------------------- -
8k k
PBFMn1:0
(
(
d
d
+
+
2
1
)
)
b1
0
Δf1
Δf2
SB
10
0
(1)
in the frame is (d-16) and the
AT90PWM81
SB+SA
Δf2
Δf2
11
0
0
Table
111
b2