Chapter 2
Hardware Overview
©
National Instruments Corporation
2-13
Considerations When Connecting the Digital I/O
The isolated trigger inputs on the NI 8255R are current sinking and
optically isolated. The following are considerations you need to make when
connecting the digital I/O.
Wiring an Isolated Input to a Sourcing Output Device
You can wire an isolated input to a sourcing output device, as shown in the
following figure. Refer to
Getting Started with the NI PCIe-8255R
for
information about switching thresholds and current requirements.
Caution
Do
not
apply a voltage greater than 30 VDC to the isolated inputs. Doing so could
damage the NI 8255R.
Figure 2-5 shows an example of connecting an isolated input to a sourcing
output device.
Figure 2-5.
Connecting isolated input to a sourcing output device
Vcc
Viso
Ciso
NI 8255R
Input
Sourcing
Output
Device
Current
Limiter
