FEATURES
Universal PCI, PCI-X, 3.3V and 5V compatible
Watchdog timer to detect computer malfunction
Optional computer power supply monitor
Optional internal computer temperature monitor
Optional measurement of computer internal temperature
Optional fan-failure detection, watchdog time-out buzzer, and opto-isolated reset output
This
multifunction card contains a watchdog timer. Additionally,
one or more options may be included on your card. These
are: a computer power supply monitor, a computer internal
temperature monitor, an optional capability to read
the temperature, a fan-speed monitor, and an on-card
buzzer to signal watchdog timeout. PCI-WDG-CSM continuously
monitors critical PC functions. When a fault occurs,
the card automatically generates outputs that can be
used either to initiate corrective action or to generate
alarms.
WATCHDOG
It's
a fact of life that computers and programs can fail.
If a computer or program fails it can cause catastrophic
damage. Even if a program merely locks up, an unattended
computer could be down for days. There are two methods
to reduce risk of computer or software failure; (a)
redundancy and (b) a watchdog circuit. Neither method
offers 100% assurance, but both of these methods reduce
risk or consequences of failure. Redundancy, a duplication
of computer circuitry, is very expensive. On the other
hand, ACCES' Watchdog card offers excellent protection
from temporary malfunctions at very low cost.
Your
application program must communicate with the watchdog
circuit at prescribed intervals. If this communication
("prompt") is missed, the Watchdog can be
programmed to initiate a computer reset (reboot). If
the reboot is successful, operation, may be returned
to the previous application program. If the failure
was temporary, proper operation is resumed. If, however,
the failure is persistent, the Watchdog will continuously
reset the computer. The more frequently the Watchdog
is prompted (and shorter Watchdog time selected), the
less time a faulty computer has to cause damage.
The
method used by the WDG-CSM card to detect loss of computer
function is as follows:
- A
type 82C54 counter/timer is used. This chip contains
three 16-bit counters. A number greater than zero
is set into the chip's Counters 0 and 1 by your
application program. The Watchdog is armed by software
command and both counters begin counting down. As
long as the computer is operating properly, both
counters will be periodically reloaded to their
original programmed values by your application program
before both counters have counted down to zero.
- If
your software fails to reload the counters, then
both counters continue counting until zero is reached
(timeout). When the counters 0 and 1 reach zero,
either the power-good line is held low for approximately
16 milliseconds (performing a hardware reset) through
a relay contact, or external lines (either relay
contacts or a de-bounced opto-isolated switch) are
active while a buzzer sounds (if enabled). When
a reset condition occurs, the reset circuit is active
until a reset pulse returns from the system bus
or power is cycled to the system.
The
clock frequency to Counter 0 is derived from the computer's
color clock and is 2.0833 MHz. (The period is 1.117
µsec.) The output of Counter 0 is used as a clock to
Counter 1. Since each counter can divide by any whole
number from 2 to 65,536 (216), the watchdog timeout
period may vary from about 10 microseconds to 4800 seconds.
The
Watchdog card can generate an interrupt request one
Counter 0 period-width before the reset timeout. For
example, if a reset period of 60 seconds is used with
a 5 milli-second delay stored in Counter 0 (the result
of a maximum value delay), an interrupt would occur
at 59.995 seconds. This gives the Interrupt handler
software 5 milliseconds to refresh the watchdog before
a reset action occurs. This should allow your software
to take corrective actions if the system software continued
to run but the software that should have reset the watchdog
had failed. Also, this timeout-imminent warning can
also be used to initiate an orderly shutdown of Windows
programs.
The
interrupt request (IRQ) output is tri-stated at a high-impedance
when it is not sending an interrupt request (1 µsec).
Thus, that IRQ number can be shared with other I/O cards
that have shareable ability. IRQ's 2 through 7, 10,
11, 12, 14, and 15 are available.
There
are several outputs from the watchdog circuit:
- Double-pole
double-throw, Form C, relay contacts on the rear
panel I/O connector
- An
opto-isolated reset output on the rear panel I/O
connector
- An
opto-isolated complement of the reset output on
the rear panel I/O connector
- A
buffered TTL CTRGATE (counter enabled) output on
the rear panel I/O connector
- TTL
reset signal on internal terminal block TB1
- The
complement of that output at terminal 3 of TB1
- A
Watchdog 56KHz heartbeat on the rear panel I/O connector
- Un-fused
5V DC output
As
noted in items b. and c. above, opto-coupler outputs
(one ON when the other is OFF) are provided for use
where relay contact bounce could be a problem. Further,
as noted in e. above, a buffered discrete output is
also provided. This output goes high to signal a watchdog
reset condition.
Finally,
a 56 KHz, TTL-level, 50% duty cycle signal is provided
at I/O connector pin 13 when the watchdog circuit is
enabled and no reset is in progress. Otherwise, this
output is in a low state.
OPTIONS
You
may order one or more options installed as mentioned
in the opening paragraph of this description. The following
paragraphs describe these options.
- Computer
Power Monitor: Three computer power supplies (+5V,
+12V, and -12V) are monitored. If one or more
of those voltages are more than +6% outside
of their nominal values, then 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: If this option is installed,
Option 01 must also be installed. This option monitors
ambient temperature inside the computer chassis.
The temperature monitor circuit compares the output
of an LM334 temperature sensor with a preset DC
voltage level. The output of the comparator circuit
can be read at a bit location of the Status Register
and, also, can cause an interrupt request if that
temperature exceeds the factory preset limit (50oC).
- Computer
Temperature Measurement: This option requires presence
of both Option 01 and 02. When this option is included,
an onboard 8 bit A/D converter provides means for
a software read of the measured temperature. Resolution
is to approx. 0.7oF.
- This
option provides three functions as follows:
- Change
of State: Differential digital inputs are accepted
through pins 17 & 18 (ISOIN0) and pins 19 & 20
(ISOIN1), are opto-isolated and reported in the
Status Register. The change-of-state also generates
an IRQ interrupt request.
- Buzzer:
The buzzer is under software control and can be
turned on by programming a "write" to
Base Address + 4 or off by programming a "write"
to Base Address +5 if Counter #2 is configured
in mode 1. Configuring Counter #2 in mode 0 will
defeat the buzzer entirely.
- Opto-Isolated
Outputs This option provides an opto-isolated
reset signal at pins 4 and 5 (Isolated Reset Output)
of the DB25F connector. An opto-isolated inverse
of the reset signal is also provided across pins
6 and 7 (Isolated NOT Reset Output) of the same
connector.
-
This option replaces the opto-isolated reset output capability of Option 04 with capability for two isolated digital outputs under computer control. Option 04 must be installed.
- Fan
Speed: This function is usable only in computers
which use fans that have a tachometer output.
If fan speed falls to unsafe levels (i.e., if
the tachometer output falls to less than 50pps),
an interrupt request is generated. (Both Options 01 and 02 must be installed)
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