B&B Electronics I-7060 - Quick Start Guide - Manual (Page 37)

Getting Started for I-7000 Series Modules
Date: Jan-08, 2002 Version 1.02 page: 37
5 Dual Watchdog
5.1 Operating Principle
All I-7000 series modules equip both a hardware module watchdog and a
software host watchdog. The I-7000 series modules are specially designed
for industry applications, and can work under any conditions. Harsh
environments may contain excessive noise or energy transient. In this case,
the modules will be adversely affected. However, the built-in
hardware
module watchdog resets the module if these forces affect the module
(see Figure 5-3-1) . Sometimes even the host-PC may be down for hardware
or software reasons. The
software host watchdog monitors the status of
host-PC. If the host-PC goes down, all output of the I-7000 series modules
will go to predefined safe states for safety protection. Refer to Figure 5-2-1 to
5-2-3) .
If the RS-485 network is open, host commands can not be sent to remote
modules. This is very dangerous in real world applications. The I-7000
output-module (AO/DO) will force the output to go to the pre-defined safe
states for safety consideration if the host watchdog is actived. This dual
watchdog feature increases the reliability of the whole system.
Dual watchdog = module watchdog + host watchdog
Host watchdog: (software/firmware)
if the host is down
!
all output goes to safe state (Safe value).
(refer to Figure 5-2-1 ~ 5-2-4).
Module watchdog: (hardware)
if the module is down
!
reset this module and the module’s output reverts to PowerOn values.
(refer to Figure 5-3-1 ~ 5-3-2).