Motorola MVME2300 Series - Manual (Page 95)

Functional Description
http://www.motorola.com/computer/literature 2-25
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Generating PCI Interrupt Acknowledge Cycles
Performing a read from the PIACK register will initiate a single PCI
Interrupt Acknowledge cycle. Any single byte or combination of bytes
may be read from, and the actual byte enable pattern used during the read
will be passed on to the PCI bus. Upon completion of the PCI interrupt
acknowledge cycle, the Raven will present the resulting vector information
obtained from the PCI bus as read data.
Endian Conversion
The Raven ASIC supports both big- and little-endian data formats. Since
the PCI bus is inherently little-endian, conversion is necessary if all MPC
devices are configured for big-endian operation. The Raven may be
programmed to perform the endian conversion described below.
When MPC Devices are Big-Endian
When all MPC devices are operating in big-endian mode, all data to/from
the PCI bus must be swapped such that the PCI bus looks big-endian from
the MPC bus’s perspective. This association is true regardless of whether
the transaction originates on the PCI bus or the MPC bus.
Figure 2-7
illustrates the concept.