BERKSHIRE PRODUCTS PC Watchdog Скачать руководство пользователя страница 6

Страница: 6 / 19

2. Operation

This device is designed to monitor PCs used in critical applications such as: File Servers, Voice Mail
Systems, ISP systems, industrial applications, etc. The idea is to make sure the PC is always available
and running; especially for systems that are not continuously monitored.

When the PC is powered up, or after a reset of the PC, the PC Watchdog will wait a preset amount of
time (2.5 minutes standard) to allow the PC to complete its reset and initialization sequence. This time
will be referred to as

ower-

elay (

POD

). After this time has expired, the PC Watchdog will

Arm

itself and start a watchdog timer running (user defined time-out period). There is a DIP Switch option
to allow the Watchdog to extend this time for PCs that need additional re-boot time.

Once the Watchdog is ready to arm itself it will check the DIP Switches and enable up to two
independent operating modes. These modes can both be active at once. They are:

•

Passive Mode

– monitors the USB bus for a 32mS polling (interrupt) transaction.

Please note that

this mode is no longer recommended.

•

Active Mode

– requires that the host communicate with the board via direct communications on a

regular basis.

Additional DIP Switches are used to set the timeout period and temperature mode. If no activity is
detected in Passive or Active Mode by the time the Watchdog timer expires, the PC Watchdog will
start its reset sequence on the PC.

The two LEDs on the Watchdog are used for status indication. The top LED provides the arming status
of the Watchdog by varying the rate at which the LED flashes. When the Watchdog resets the PC it
will turn on the bottom LED and leave it on which provides an indication that at least one Watchdog
reset has occurred, possibly more. In Active Mode the PC can turn this LED off and also get a count of
the number of resets that have occurred. The bottom LED will also flash (on or off) once per second for
a tenth of a second if a Watchdog timer reset ('tickle”) event occurred in the prior second.

Note: If you stop your application program or you reset the PC with CTL-ALT-DEL, then be sure to
disable the Watchdog by unplugging the reset cable or remove power by disconnecting he USB cable.
Otherwise it may count down and reset your PC at an inopportune time!

The temperature circuit on the board will monitor the internal temperature of the PC. There are two
standard temperature trip points available:

(115

) and

C (

133

F). At the first trip point the PC

Watchdog board can activate the Aux relay if the option is selected. It will also activate an audible
alarm. At the second trip point the PC Watchdog can optionally activate the reset relay to stop the PC
from further processing.

There is an option to allow shifting the trip points higher via software control. The trip points can be
increased in

increments up to

C (

171

and

(189

F).