ADLINK Technology PCI-8254, User Manual

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Motion Control Theory 173
PCI-8254 / PCI-8258
c. Mode 3: PWM frequency mode with fixed duty cycle
This control mode changes PWM frequency according to speed at
fixed PWM duty cycle. As shown in figure below, the duty cycle
W
1
/T
1
, W
2
/T
2
and W
3
/T
3
are the same under varying speed while
their frequency and pulse width changes according to the VAO
table.
1. Set up control mode: Use APS_set_vao_param( ) to set
up
value of VAO_TABLE_OUTPUT_TYPE
parameter to 0x3
.
2. Set up fixed PWM duty cycle:
Use APS_set_vao_param( ) to set up parameter
VAO_TABLE_PWM_Config
in unit of %. Valid range is
0.05% ~ 100% now.
4.10.3.3 VAO Table
The VAO table is designed to give speed-based PWM power for
VAO controller to control actual PWM output signal. The VAO
module features eight VAO tables for layered cutting. Each table
may contain up to 32 speed-power pairs. See below for details on
calculating speed-based power value. In figure below the X-axis is
for composite speed of axes and the Y-axis its relevant PWM
power. Please note the unit of power varies with control modes.
Take example. If the control mode is set to mode 1: PWM mode
the corresponding power is PWM duty cycle; if the control mode is
set to mode 2: PWM frequency mode with fixed width then its
power is PWM frequency. If the composite speed V
X
is available,
its corresponding power P
x
can be interpolated as
P
X
= (P
3
– P
2
) * (V
X
– V
2
) / (V
3
– V
2
) + P
2