page 90
Calculation of the RELOAD value
The reload value of the internal PWM counter is calculated as
follows based on the input DIV64:
DIV64 = 0: f
PWM
= 2.50 MHz / (10000 Hex - Reload)
DIV64 = 1: f
PWM
= 156.25 kHz / (10000 Hex - Reload)
The input DIV64 has to be set to 0 or 1 depending on whether a
high or a low PWM frequency is required. For PWM frequencies
< 39 Hz DIV64 has to be set to 1 so that the reload value does
not get smaller than 0000 Hex.
Example
The PWM frequency should be 200 Hz.
2.5 MHz
----------- = 12500
⇒
30D4 Hex
200 Hz
Reload value
⇒
10000 Hex - 30D4 Hex = CF2C Hex
The permissible range for the PWM value is
from CF2C Hex to FFFF Hex
The comparative value at which the output switches has to be
between CF2C Hex and FFFF Hex.
The PWM frequency is the same for all PWM outputs.
Functions PWM and PWM100 must not be mixed.
This results in the following pulse / break ratios:
minimum pulse / break ratio (0 % on): FFFF Hex
maximum pulse / break ratio (100 % on): CF2C Hex
12500 intermediate values (PWM values) are possible between
maximum and minimum.
PWM dither
In some hydraulic valve types the PWM frequency has to be
superimposed by a so-called dither frequency (jitter frequency).
If these valves were triggered with a constant PWM value over a
longer period of time they might stick due to the high system
temperatures. To prevent this, the PWM value is increased or
decreased by a defined value (DITHER_VALUE) based on the
dither frequency. As a result, the constant PWM value is
superimposed by a beat with the dither frequency and the
amplitude DITHER_VALUE. The dither frequency is stated as a
ratio (divider, DITHER_DIVIDER) of the PWM frequency
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