Advantech SOM-Express Design Guide
Chapter 5 Carrier Board Design Guidelines
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SOM-Express
SMB_DAT
SMB_CLK
Carrier board
VCC
1
2
3
4
SMB
Connecto
r
Figure 5-40 SMB Bus Connections
5.9.4 Power Good/Reset Input
The SOM-Express Power OK Input (PWR_OK) may be attached to an external
power good circuit if desired, or used as a manual reset input by grounding the pin
with a momentary-contact pushbutton switch. If an external circuit asserts this signal,
it should be driven by an open-drain driver and held low for a minimum of 15mS to
initiate a reset. Use of this input is optional. The SOM-Express module generates its
own power-on reset based on an internal monitor on the +5 V input voltage and/or
the internal power supply.
Figure 5-41 Power OK/Reset Input Connections
5.9.5 WDT
SOM-Express provides a watch-dog function via the pin WDT. It can prevent the
system from shutting down for a long time. It can generate a signal to reset the
system. In SOM-Express, the WDT is low active. Figure 5-42 shows an example of
the watch-dog circuit.
