Sensoray 2518 - Manual (Page 7)

Sensoray Model 2518/2519 Ethernet Smart A/D™ 4 Introduction
2.4 Watchdog Timer
Two watchdog timers are implemented on the Ethernet
base board. One timer is implemented in hardware and
the other in software. Either of the timers will invoke a
reset of the entire Smart A/D™ unit if a time-out occurs.
• The hardware watchdog timer will time out if it is not
kept refreshed by the local network processor. This
timer guards against disruptions due to local power
transients and circuit failures.
• The software watchdog timer will time out if no
personal network packets have been received for a
period of ten seconds. This timer protects against
system faults such as network and client failures.
2.5 Reset State
A hardware reset of the Ethernet base unit is invoked in
response to any of the following events:
• Power-up.
• Watchdog time-out.
Smart A/D™ daughter boards experience a hardware
reset whenever the Ethernet base unit performs a
hardware reset. In addition, invoking a soft reset (see
Section 6.3.1) on a specific Smart A/D™ daughter board
will cause that board to undergo a hardware reset.
2.5.1 Reset State
Upon the occurrence of a reset, all Smart A/D™ daughter
boards are in the default state as described below:
q Standard speed mode (22ms/channel) is selected.
q 60Hz rejection mode is active.
q
All channels are enabled for scanning.
q Sensor data values are reset to zero. Sensor data is
not available immediately after a board reset. The
maximum elapsed time that must pass before new
sensor data becomes available is equal to 35 channel
slot times. Details of channel slot timing can be
found in Section 9.2
q Channels are configured for the 5-volt input range,
with 500µV resolution.
q Software filter constants are set to zero (disabled).
q
Alarm threshold limit values are indeterminate.
q
All channel alarms are disabled.
q All channels are programmed to fail high upon
open-sensor detection.
2.6 Visual Indicators
2.6.1 Fault Indicator
A red light-emitting diode (LED), located on each Smart
A/D™ daughter board, is used as a status indicator. This
LED is energized as a result of any of the following
conditions:
• A board reset is in progress.
• A board fault has been detected.
When a Smart A/D™ is functioning normally, its LED is
energized for approximately one-half second in response
to either a hardware or a soft reset. In the case of
hardware resets, this time period may be longer than 0.5
seconds due to stretching of the reset signal on the local
PC/104 bus.
If the LED is persistently energized, there may be a
hardware fault on the A/D board. In this case, be sure to
check all sensor connections, board orientation and
seating, etc. before concluding that the board has a fault.
2.6.2 Heartbeat Indicator
The model 2509 base board includes a LED, labeled
“RUN,” that flashes on and off at approximately two
Hertz. When flashing at this rate, the RUN LED
indicates that the network processor is functioning
normally.
2.6.3 Network Status Indicators
Four LEDs on the model 2509 Ethernet base board are
used to indicate the status of the Ethernet interface:
• XMT — Active for approximately 0.25 seconds when
the 2509 transmits a packet.
• RCV — Active for approximately 0.25 seconds when
the 2509 receives a packet addressed to its Ethernet
address.
• LNK — Active whenever Link pulses are being
detected on the wire.
• SEL — Active for approximately 0.25 seconds when
the board’s network processor accesses the Ethernet
interface circuitry.