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A32
USR
SUP
Programming the Local-Bus-to-VMEbus Map Decoders
This section includes programming information on the local-bus-to-
VMEbus map decoders and the GCSR base address registers.
The local-bus-to-VMEbus interface allows onboard local bus masters
access to off-board VMEbus resources. The address of the VMEbus
resources as viewed from the local bus is controlled by the local bus slave
map decoders, which are part of the local-bus-to-VMEbus interface. Four
of the six local-bus-to-VMEbus map decoders are programmable, while
the two I/O map decoders are fixed. The first I/O map decoder provides an
A16/D16 or A16/D32 space at $FFFF0000 to $FFFFFFFF which is the
VMEbus short I/O space. The second I/O map decoder provides an
A24/D16 space at $F000000 to $F0FFFFFF and an A32/D16 space at
$F1000000 to $FF7FFFFF.
A programmable segment may vary in size from 64KB to 4GB in
increments of 64KB. Address translation for the fourth segment is
provided by the address translation registers which allow the upper 16 bits
of the VMEbus address to be provided by the address translation address
register rather than the upper 16 bits of the local bus.
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When this bit is high, the first map decoder responds to
VMEbus A32 (extended) access cycles. When this bit is
low, the first map decoder does not respond to VMEbus
A32 access cycles.
When this bit is high, the first map decoder responds to
VMEbus user (non-privileged) access cycles. When this
bit is low, the first map decoder does not respond to
VMEbus user access cycles.
When this bit is high, the first map decoder responds to
VMEbus supervisory access cycles. When this bit is low,
the first map decoder does not respond to VMEbus
supervisory access cycles.
LCSR Programming Model
2-37
2
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