P104-WDG-CSM User Manual
7
P104-WDG-CSM: Standard Watchdog with Computer Status Monitor
This model provides a fully programmable watchdog with open collector outputs that
can reset the computer. It also contains various I/O to monitor and control the health of the
computer. It contains computer power monitoring, computer temperature monitoring and
measurement, isolated inputs and isolated outputs. (See Chapter 5 for 40-pin connector
information.) The following I/O connections are provided:
a. Two isolated digital inputs, current limited.
b. Two isolated digital outputs, current limited.
c. Two non-isolated digital outputs in parallel to isolated digital outputs.
d. Reset pushbutton input, TTL, active LOW, buffered.
e. Fused external 5VDC power for external LED.
Computer Power Monitor
The +5VDC computer power supply may be monitored. If the voltage varies by more than
+6%, two bits of a Status Register indicate whether there is an overvoltage or an
undervoltage. In addition, an interrupt request can be generated.
Computer Temperature Monitor
This feature monitors ambient temperature in the area of the watchdog circuit board. The
temperature monitor circuit compares the output of an on-board LM334 temperature sensor
with a preset DC voltage level. The output of the circuit can be read at bit 1 of the Status
Register and can also cause an interrupt request if that temperature exceeds the factory
preset limit (approx. 50 °C).
Computer Temperature Measurement
The on-board LM334 temperature sensor output is input to a dedicated onboard 8 bit A/D
converter which provides means for a software read of the measured temperature.
Opto-Isolated Outputs
Software can control two optically isolated outputs. Each has a transistor with a 330 current
limiting resistor on the collector and an uncommitted emitter. Also, two non-isolated digital
outputs at pin 2 of connector P1 (LED/Digital 1) and pin 6 of connector PI(LED/Digital 2), are
available for driving an external device such as a LED (up to 15mA sink or source). These
signals are in parallel with the isolated outputs making the isolated outputs activated with the
non-isolated digital outputs. OUT1 at pin 28 connects to a 330 ohm resistor which is
connected to the collector of an opto-coupled transistor. Pin 29 connects to the emitter. As
much as 18 volts and 100mA can be switched, reverse bias should be avoided. Out2 at pins
32 and 33 are an identical circuit.
Push Button Reset Input
The Push Button Reset buffered input (P1 pin 16) has a 4.7k pull-up.
Fused External Power LED
Pin 4 has a 0.3A (300mA) (at room temperature) resettable fuse connected to +5V. At +85C
this fuse trips at 0.15A (150mA), at 0 degrees C this fuse trips at 0.6A (600mA).
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