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National Instruments Corporation
9
USB-6525 User Guide and Specifications
Programmable Power-Up Output States
The default power-up state of the digital output lines is logic low, which
opens the solid-state relays. The lines on output ports are user-configurable
for logic high (closed relay) or logic low (open relay). User-configurable
power-up states are useful for ensuring that the NI 6525 powers up in a
known state.
To use MAX (recommended) to program the power-up states, select
the device and click the
Properties
button. Refer to the software
documentation for information about how to program the power-up states
using NI-DAQ with LabVIEW or other National Instruments application
development environments (ADEs).
Watchdog Timer
The watchdog timer is a software configurable feature used to set critical
outputs to safe states in the event of a software failure, a system crash, or
any other loss of communication between the application and the NI 6525.
When the watchdog timer is enabled, if the NI 6525 does not receive a
watchdog reset
software command within the time specified for the
watchdog timer, the outputs go to a user-defined safe state and remain in
that state until the watchdog timer is disarmed by the application and new
values are written, the NI 6525 is reset, or the computer is restarted. The
expiration signal that indicates an expired watchdog will continue to assert
until the watchdog is disarmed. After the watchdog timer expires, the
NI 6525 ignores any writes until the watchdog timer is disarmed.
You can set the watchdog timer timeout period to specify the amount of
time that must elapse before the watchdog timer expires. The counter on the
watchdog timer is configurable up to (2
32
– 1) × 40
μ
s
1
before it expires.
Digital I/O
USB-6525 has eight channel-to-channel optically isolated inputs,
P1.<0..7>, and eight channel-to-channel optically isolated solid-state relay
outputs, P0.<0..7>. P1.7/PFI 0 can also function as a 32-bit counter. Refer
to the
Event Counter
section for more information about the counter.
Optically Isolated Inputs
The USB-6525 provides eight channels of isolated digital inputs. These
inputs consist of an optocoupler, a depletion-mode MOSFET-based
current-limiting circuit, and Schottky diode.
1
The accuracy of the sample clock is ±1.5%.
