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PCI/PMC E
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ANUAL
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PCI-P0 S
YSTEM
S
LOT
T
ERMINATION
The PMC-605 terminates signals as required for a PCI System Slot Controller when the
TERMDIS signal is connected directly to Ground. The System Slot termination is disabled
when the TERMDIS signal is connected directly to Vcc.
The term System Slot Controller refers to a PMC-605 when it is configured to provide PCI
bus arbitration on the PCI-P0, distribute the PCI Bus clock across the backplane, and provide
termination of specific signals.
In a multi-slot system, the bus is normally 'parked' on the System slot by the arbiter when
the arbiter assigns a card default ownership of the bus. This ensures that the majority of the
signals on the bus are driven but reduces power requirements by removing the necessity of
each card having pull-ups. Some signals, however, need to be free for any card to assert.
These signals cannot be left floating or driven and hence the System Controller provides the
pull-ups (terminations) for these signals. On the PMC-605 these signals are: FRAME, TRDY,
IRDY, DEVSEL, STOP, SERR, PERR and INTA.
I
NTERRUPTS
The 21554 PCI-to-PCI Bridge device does not accept interrupts although it may generate
them to either the primary bus (P0 side) or secondary bus (host processor side). Any P0 bus
interrupt is seen directly by the basecard, as long as bit D5 of the LCSR is set to a '1' - if bit
D5 of the LCSR is set to a '0' (default), then the P0 bus interrupt is withheld from the
basecard.
Interrupts are passed between processor cards using “doorbell” registers in the 21554.
Interrupts from non-intelligent cards use the INT line on the PCI-P0 bus and are buffered
through the PMC-605 card to the host processor card.
Cross Reference
The TERMDIS signal referred to above is connected to Ground or Vcc via the 2 or 3 slot PCI-
P0 Development Backplane (part number BPL-605-002 or BPL-605-003). The PMC-605
terminates signals when placed in the PCI-P0 backplane’s System Slot. It does not
terminate signals when placed in a Peripheral Slot. See “System Slot Termination Jumper
Settings” on page 3-5 of this manual for information on configuring signal termination
settings when using the PMC-605 with the PCI-P0 Development Backplane.
Caution
The TERMDIS signal must not be left open circuit because it is an input to the CPLD which
does not have a pull-up on it. Inputs should not be left floating.
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