emphase
applied engineering
Emphase Watchdog Timer
User Manual
WDT-01
Revision 1
Datasheet, January 2008
Revision 1.0
emphase
applied engineering
Emphase WDT-01
1.Introduction
General Description
The WDT-01 is a watchdog timer module that supervises microprocessor activity. It resets a nonresponsive system after a timeout period. During normal operation, the microprocessor should repeatedly toggle the watchdog input (WDI) before the selected watchdog
timeout period elapses. This demonstrates that the system is processing code properly. If the system does not provide a valid watchdog input transition before the timeout period expires, the watchdog timer sends a reset signal to the system. The WDT-01 watchdog
timer increases system reliability through notification of code execution errors.
Key Features
•
Precision Watchdog Timer Module for Critical System Applications
•
Small Footprint Module: 0.7” x 1.7” (17 x 43 mm)
•
Compatible with most Standard PC Mainboards
•
Pin-Selectable Watchdog Timeout Period (1 sec. or 10 sec.)
•
Pin-Selectable Watchdog Startup Delay Period (60 sec. or First Pulse)
•
Operating Voltage +5V
•
Wide input 5–12V Watchdog Input signal (from COM port or GPIO)
•
Header Pins for Optional Manual Reset Switch
•
RoHS compliant
•
Includes 2 jumpers & 3 pin header cables (200 mm)
Applications
Automotive/Mobile Computing
Remotely Deployed Systems
Critical Systems Monitoring
Embedded Control Systems
Industrial Control
Networking
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Revision 1.0
Datasheet, January 2008
emphase
applied engineering
Emphase WDT-01
II.
Logic Diagram
Figure 1 below shows the Logic Diagram of the Emphase WDT-01 Watchdog Timer.
PWR
(+5 V)
Watchdog
TImer
Reset
Generator
Reset
Mainboard
Reset
GND
WDI
Optional
Reset Switch
COM port DTR
or GPIO pin
(5–12 V)
Figure 1: Logic Diagram
III.Connection Diagram
Please be careful to use the right polarity (+ / -) when connecting the watchdog timer. Failure to do so will void the warranty and
may result in damage to the timer or the mainboard.
Figure 2 below shows the connection diagram of the Emphase WDT-01.
PWR
WDI
reset
JP2
JP1
Figure 2: Connection Diagram
Table 1: Pin Descriptions
Connection
Pins
Description
Power
PWR
Connect a 5V power source from the motherboard or the power supply to the PWR header of the watchdog timer. Connect
both 5V (+) and GND (-)
Watchdog Input
WDI
The watchdog input is the trigger for the watchdog timer. After each pulse the timer restarts counting. It accepts a wide
5–12V level input. The WDI + pin can be connected to any output from the mainboard. Examples are the DTR pin on a COM
port or a GPIO pin. Connecting WDI - is optional.
Reset
RST
Connect one of the RST + pins to the reset header pins on the mainboard. The watchdog activates the reset signal if no pulse
has been received within the set timeout period. Connecting RST - is optional.
The second RST header pair can optionally be used to connect a manual reset switch.
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Revision 1.0
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emphase
applied engineering
Emphase WDT-01
IV. Settings
The watchdog timer has three different modes of operation. These are selectable by setting the jumpers JP1 and JP2. See Table 2 for
the available settings.
Table 2: Jumper Settings
Jumper Setting
JP1
JP2
1–2
2–3
2–3
1–2
1–2
1–2
2–3
2–3
Drawing
JP2
JP1
JP2
JP1
JP2
JP1
JP2
JP1
*Delay is variable due to component tolerance.
Startup Delay
Timeout Period
Min
MAX
MIN
MAX
60 seconds*
180 seconds*
1 second*
3 seconds*
60 seconds*
180 seconds*
10 seconds*
30 seconds*
First Edge
--
10 seconds*
30 seconds*
Disabled
Disabled
Disabled
Disabled
Watchdog Startup Delay Period
The Startup Delay Period sets the initial startup delay after powering on the system. With a 60-second startup delay, the watchdog
timer starts monitoring the watchdog input (WDI) 60 seconds after the system starts, or after a reset. In First Edge mode, the watchdog timer is activated only after the first pulse (edge) has been detected on the watchdog input (WDI). This allows the operating
system and application to start before the watchdog timer is activated.
Watchdog Timeout Period
The watchdog timeout period is the maximum interval between phase changes on the watchdog input (WDI). If this interval is
exceeded, the watchdog timer will send a reset pulse to the mainboard. The watchdog timeout interval can be set to a 1-second or
10-second interval.
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Datasheet, January 2008
emphase
applied engineering
Emphase WDT-01
V. Timing Diagram
Figure 3 below shows the timing diagram of the Emphase WDT-01 Watchdog Timer.
Watchdog
timeout
period
Startup delay Period
Startup delay Period
Watchdog
timeout
period
Watchdog
input
A
A
A
B
C
D
E
F
Reset
A
B
C
D
E
F
Reset
Pulse
Figure 3: Timing Diagram
Transitions on Watchdog Input ignored during Startup Delay period.
Watchdog Timer starts after Startup Delay.
Transition occurs before Watchdog Timeout period. Timer clears, then restarts timer.
Watchdog times out, Reset pulse is sent to mainboard.
System and Watchdog timer restarts.
Watchdog Input is ignored during Startup Delay.
VI.Software Considerations
When implementing the microprocessor’s watchdog strobe code,
quickly switching WDI low-high and then high-low (minimizing
WDI high time) can be desirable for controlling current consumption.
However, a more effective way of using the watchdog function should
be considered.
A low-high-low WDI pulse within a given subroutine prevents the
watchdog from timing out. However, if the subroutine becomes stuck
in an infinite loop, the watchdog cannot detect this because the subroutine continues to toggle WDI. A more effective coding scheme for
detecting this error involves using a slightly longer watchdog timeout.
In the program that commands the subroutine, WDI is originally
set at high. When the subroutine gets called by the program, it sets
WDI to low. If the program executes without error, WDI is toggled
high-low during every loop of the program. If the subroutine enters
an infinite loop, WDI is kept low, the watchdog times out, and the
microprocessor is reset.
Start
Set WDI
High
Reset
Program
Code
Subroutine or
Program Loop
Set WDI low
Infinite loop:
Watchdog
Times Out
Return
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Revision 1.0
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emphase
applied engineering
Emphase WDT-01
VII. Specifications
Watchdog Power Usage
To minimize watchdog power consumption, leave WDI low for the majority of the watchdog timeout period. Pulsing WDI low-highlow at a low duty cycle reduces the power consumption.
Input Voltage: +5 V ±10%
Input Current:
<1 mA Typ.
Output Current: 20 mA Max.
Operating temperature range: 0°C ~ +60°C
Storage temperature range:
-40°C ~ +125°C
ESD Caution
The WDT-01 is an ESD (electrostatic discharge) sensitive device. Electrostatic
charges as high as 4,000V readily accumulate on the human body and test
equipment; these can discharge onto the device without detection. Although
this product features proprietary ESD protection circuitry, permanent damage
can occur on devices subjected to high-energy, electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
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