Advantech SOM-Express Design Guide
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Chapter 5 Carrier Board Design Guidelines
The SPKR output from the SOM-Express module is a CMOS level signal. It can
control an external FET or logic gate that drives an external PC speaker. The SOM-
Express modules SPKR output should not be directly connected to either a pull-up or
a pull-down resistor. The SPKR signal is often used as a configuration strap for the
core chipset in SOM-Express modules. A pull-up or pull-down on this signal can
override the internal setting in the module and result in malfunction of the module.
5.9.2 I2C Bus
SOM-Express
I2C_DAT
I2C_CK
Carrier board
VCC
1
2
3
4
I2C
Figure 5-39 I2C Bus Connections
Most SOM-Express modules provide a software-driven I2C port for communication
with external I2C slave devices. This port is implemented on SOM-Express Pins
I2C_DAT and I2C_CK.
5.9.3 SMBus
Most SOM-Express modules provide a SMBus port for communication with external
SMBus slave devices. This port is also used internally in the SOM-Express module to
communicate with onboard SMBus devices such as the SPD EEPROMs on DIMMS,
clock-generator chips, and hardware monitoring devices. The port is externally
available on the SOM-Express pins SMB_DAT and SMB_CK. The addresses for any
external SMBus devices must be chosen so that they do not conflict with the
addresses that are used internally in the SOM-Express module. If the device offers
externally controllable address options, it is desirable to implement carrier board
resistor straps to allow the device to be set to at least two possible SMBus addresses.
