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Functional Description
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PPC Bus Timer
The PPC bus timer allows the current bus master to recover from a lock-
up condition caused when no slave responds to the transfer request.
The time-out length of the bus timer is determined by the MBT field in the
Global Control/Status Register.
The bus timer starts ticking at the beginning of an address transfer (TS*
asserted), and if the address transfer is not terminated (AACK* asserted)
before the time-out period has passed, the Raven will assert the MATO bit
in the PPC Error Status Register, latch the PPC address in the PPC Error
Address Register, and then immediately assert AACK*.
The MATO bit may be configured to generate an interrupt or a machine
check through the MEREN register.
The timer is disabled if the transfer is intended for PCI. PCI bound
transfers will be timed by the PCI master.
PCI Interface
The Raven PCI Interface is designed to connect directly to a PCI Local Bus
compliant I/O bus.
The PCI interface may operate at any clock speed up to 33 MHz. The
PCLK input must be externally synchronized with the MCLK input, and
the frequency of the PCLK input must be exactly half the frequency of the
MCLK input.
PCI Map Decoders
The Raven contains four programmable decoders which provide windows
into the PPC bus from the PCI bus. The most significant 16 bits of the PCI
address is compared with the address range of each map decoder, and if the
address falls within the specified range, the access is passed on to the PPC
bus. For each map, there is an independent set of attributes. These
attributes are used to enable read accesses, enable write accesses, enable
write posting, and define the PPC bus transfer characteristics. Each map
decoder also includes a programmable 16-bit address offset. The offset is