ADLINK PCI-7442 - Manual (Page 42)

30 Operation theory
3.3 Isolated digital output channels
The common ground connection of isolated digital output is shown
in the figure below. When the isolated digital output goes ON, the
sink current will be conducted through the power MOSFETs. When
the isolated digital output goes OFF, no current is conducted to
flow through the power MOSFETS. Take note that when the load
is of an inductance nature such as a relay, coil or motor, the VDD
pin must be connected to an external power source. The extra
connection is utilized for the fly-wheel diode to form a current-
release closed loop, so that the MOSFETs are protected from any
high reverse voltage which can be generated by the inductance
load when the output is switched from ON to OFF. In addition, you
can read back the 64-/128-CH IDO statuses to check if the sta-
tuses meet your purpose.
Figure 3-4: Common Ground Connection of Isolated Digital Output
The PCI-7442/PCI-7444 provides three special functions for safety
measures. First, the PCI-7442/PCI-7444 could automatically con-
figure the 64-/128-CH DO initial statuses when powering up. Sec-
ond, you can direct the PCI-7442/PCI-7444 to hold the DO
statuses and avoid its power-up initial configuration state after a
hot system reset. Third, you can direct the PCI-7442/PCI-7444 to
automatically configure the 64-/128-CH DO safety statuses when
a WDT interruption asserts.
x: 0~63
x: 0~127