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User Guide XB1 COM Express Module
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Thermal Considerations
In order to avoid malfunctioning of the XB1 COM Express Module, take care of appropriate cooling
of the processor and system, e.g. by a cooling fan suitable to the maximum power consumption of
the CPU chip actually in use. Please note, that the processors temperature is steadily measured by a
special controller (LM87), attached to the onboard SMBus
®
(System Management Bus). A second
temperature sensor internal to the LM87 allows for acquisition of the boards surface temperature.
Beside this the LM87 also monitors most of the supply voltages. A suitable software to display both,
the temperatures as well as the supply voltages, is MBM (Motherboard Monitor), which can be
downloaded from the web. After installation, both temperatures and voltages can be observed
permanently from the Windows taskbar.
The XB1 COM Express Module is equipped with a passive heatsink (heat-spreader). In addition, a
forced airflow through the system enclosure by a suitable fan unit is highly recommended (>15m
3
/h
or 200LFM around the CPU module). As an exception, the XB1-100 (ULV Celeron M 1GHz) can be
operated with natural convection only. Be sure to thoroughly discuss your actual cooling needs with
EKF. Generally, the faster the CPU speed the higher its power consumption. For higher ambient
temperatures, consider increasing the forced airflow to 400 or 600LFM.
The table showing the supported processors above give also the maximum power consumption (TDP
= Thermal Design Power) of a particular processor. Fortunately, the power consumption is by far
lower when executing typical Windows or Linux tasks. The heat dissipation may increase considerably
when e.g. rendering software such as the Acrobat Distiller is executed.
The Pentium M processors support Intel's Enhanced SpeedStep® technology. This enables dynamic
switching between multiple core voltages and frequencies depending on core temperature and
currently required performance. The processors are able to reduce their core speed and core voltage
in up to 8 steps down to 600MHz. This leads to an obvious reduction of power consumption (max.
7.5W @600MHz) resulting in less heating. This mode of lowering the processor core temperature is
called TM2 (TM=Thermal Monitor). Note, that TM2 is not supported by Celeron M processors.
Another way to reduce power consumption is to modulate the processor clock. This mode (TM1) is
supported also by the Celeron M processors and is achieved by actuating the 'Stop Clock' input of the
CPU. A throttling of 50% e.g. means a duty cycle of 50% on the stop clock input. However, while
saving considerable power consumption, the data throughput of the processor is also reduced. The
processor works at full speed until the core temperature reaches a critical value. Then the processor
is throttled by 50%. As soon as the high temperature situation disappears the throttling will be
disabled and the processors runs at full speed again.
A similar feature is embedded within the Graphics and Memory Controller (GMCH) i915GM. An on-
die temperature sensor is used to protect the GMCH from exceeding its maximum junction
temperature (T
J,max
=105°C) by reducing the memory bandwidth.
These features are controllable by BIOS menu entries. By default the BIOS of the XB1 COM Express
Module enables mode TM2 which is the most efficient.