RAM5006E-016 Emerson Network Power, RAM5006E-016 Datasheet - Page 100

• Manufacturer Part Number: RAM5006E-016
• Manufacturer: Emerson Network Power

Specifications of RAM5006E-016

• Lead Free Status / RoHS Status: Compliant

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7 Programming the MVME5100
PCI Domain
VMEbus Domain
MVME51005E Single Board Computer Installation and Use (6806800A38B)
The PCI bus is inherently little-endian. All devices connected directly to the PCI bus operate in
little-endian mode, regardless of the mode of operation in the processor’s domain.
PCI and Ethernet
Ethernet is byte-stream-oriented; the byte having the lowest address in memory is the first one
to be transferred regardless of the endian mode. Since the PHB maintains address invariance
in both little-endian and big-endian mode, no endian issues should arise for Ethernet data. Big-
endian software must still take the byte-swapping effect into account when accessing the
registers of the PCI/Ethernet device, however.
Role of the Universe ASIC
Because the PCI bus is little-endian while the VMEbus is big-endian, the Universe PCI/VME bus
bridge ASIC performs byte swapping in both directions (from PCI to VMEbus and from VMEbus
to PCI) to maintain address invariance, regardless of the mode of operation in the processor’s
domain.
The VMEbus is inherently big-endian. All devices connected directly to the VMEbus must
operate in big-endian mode, regardless of the mode of operation in the processor’s domain.
In big-endian mode, byte-swapping is performed first by the Universe ASIC and then by the
PHB. The result is transparent to big-endian software (a desirable effect).
In little-endian mode, however, software must take the byte-swapping effect of the Universe
ASIC and the address reverse-rearranging effect of the PHB into account.
For further details on endian considerations, refer to the MVME5100-Series Single Board
Computer Programmer’s Reference Guide.