Pci Bus Interface - Motorola MVME2600 Series Reference Manual

Functional Description
Universe is also compatible with all VMEbus modules conforming to pre-
VME64 specifications. As VMEbus master, the Universe supports Read-
Modify-Write (RMW), and Address-Only-with-Handshake (ADOH) but
does not accept RETRY* as a termination from the VMEbus slave. The
ADOH cycle is used to implement the VMEbus Lock command allowing
a PCI master to lock VMEbus resources.
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PCI Bus Interface

Universe as PCI Slave
Read transactions from the PCI bus are always processed as coupled. Write
transactions may be either coupled or posted, depending upon the setting
of the PCI bus slave image. (Refer to PCI Bus Slave Images in the Universe
User Manual.) With a posted write transaction, write data is written to a
Posted Write Transmit FIFO (TXFIFO) and the PCI bus master receives
data acknowledgment from the Universe with zero wait states. Meanwhile,
the Universe obtains the VMEbus and writes the data to the VMEbus
resource independent of the initiating PCI master. (Refer to Posted Writes
in the Universe User Manual for a full description of this operation.)
To allow PCI masters to perform RMW and ADOH cycles, the Universe
provides a Special Cycle Generator. The Special Cycle Generator can be
used in combination with a VMEbus ownership function to guarantee PCI
masters exclusive access to VMEbus resources over several VMEbus
transactions,and. (Refer to Exclusive Accesses and RMW and ADOH
Cycles in the Universe User Manual for a full description of this
functionality.)
Universe as PCI Master
The Universe becomes PCI master when the PCI Master Interface is
internally requested by the VME Slave Channel or the DMA Channel.
There are mechanisms provided which allow the user to configure the
relative priority of the VME Slave Channel and the DMA Channel.
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