Model 466-1 Adapter
Adapter Functions 7
1.4 Dual Port RAM
Dual Port RAM is an optional memory card that attaches to the VMEbus
adapter card and appears to both systems as simply more memory. The
address of Dual Port RAM is independently set on each adapter card, and may
be set to respond to one address range in one system and a different range in
the other. Both systems can access the memory at the same time with the
adapter arbitrating simultaneous accesses.
The following sizes of Dual Port RAM are available from SBS: 128K and 8M
byte cards.
All Dual Port RAM cards are designed to ignore unused upper address
bits. However, bits A23 and above must select the Dual Port RAM
window. Therefore, for a 1M byte memory Dual Port RAM card, only
Address Lines A19 - A0 are significant; Address Lines A19 and above
are ignored.
1.5 System Controller Operation
The Model 466-1 adapter has the ability to act as a link between the two
chassis even when the VMEbus chassis has no processor present. This form
of operation is called
System Controller Mode.
System Controller Mode is selected on the adapter card installed in slot one of
the chassis that has no processor.
System Controller Mode is configured by setting the
SYS
jumper block to
drive the system clock, system reset, and the Bus Error (BERR) global
timeout. An adapter card may be configured to be a single-level (SGL) bus
arbiter or a four-level bus arbiter in priority (PRI) or round-robin (RRS) mode.
A priority arbiter provides requesters preferential control of the data transfer
bus over other levels. By definition, BR3 has highest priority, and BR0 is the
lowest. When two or more requests are pending, the arbiter assigns control of
the bus in the appropriate order by granting the bus in this sequence.
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