rtd cpuModules CMA24BT, Руководство пользователя

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BDM-610000087 Rev A Chapter 2: Getting Started 25
Connecting to the PCI-104 (PCI) Bus
There are two additional considerations to make when using the PCI bus:
•
Slot selection switches on add-in boards
•
PCI bus signaling levels
Slot Selection Switches
Unlike PCIe cards, PCI-104 expansion cards have a “slot” selection switch or jumpers. In total, there are 4
PCI cards that can be stacked onto the cpuModule with switch positions 0 through 3. The distance from the
CPU determines these switch settings. The card closest to the CPU is said to be in slot 0, the next closest
slot 1 and so on to the final card as slot 3.
The “slot” setting method may vary from manufacturer to manufacturer, but the concept is the same. The
CPU is designed to provide the correct delay to the clock signals to compensate for the bus length. The
correct switch setting ensures the proper clock delay setting, interrupt assignment, and bus grant/request
channel assignment. Refer to the expansion board’s manual for the proper settings. Each expansion card
must be in a different slot.
PCI Bus Signaling Levels
The PCI bus can operate at +3.3 V or +5 V signaling levels. The default PCI bus signaling level is +3.3 V.
For more information, contact RTD Technical Support.
WARNING You will have to ensure that all your expansion cards can operate together at a
single signaling level.
Note Although it is possible to power the cpuModule through the Auxiliary Power connector,
the preferred method is to power it through the bus connector from a power supply in the
stack. The cpuModule can have large current transients during operation, which make
powering it through wires difficult. Powering through the bus eliminates such problems as
voltage drop and lead inductance.