Multibus P2 Connector; Card Insertion Order - Sun Microsystems Sun Workstation 100U System Manager's Manual

Hardware Configuration and Expansion
Sun 100/150 Installation Manual
you add any additional DMA cards to the system. Note that non-DMA cards, such as Sun
display controllers, Sun Ethernet controllers, and many other Multibus cards, are not Multibus
masters and do not come under this restriction.
In the Multibus mastering scheme, the order of the cards in the card cage determines their
priority. Slot number 1 is the highest priority bus master, and slot number 7 is the lowest. Bus
master devices in the 100U card cage must be in electrically adjacent slots - this means that
they must either be physically adjacent, or separated by a board which passes the bus arbitra-
tion signal straight through. Currently, the only SUD boards which are 'transparent' in this
sense are the 1-MByte Memory board and Rev. C or 'greater' 1/4" Tape Controller boards.
These boards may therefore be inserted between bus masters.
8.1.2. 100U Multibus P2 Connector
The P2 bus is a high-speed synchronous memory bus that allows memory access without wait
states. The design of the connector for the P2 bus requires that the processor board and the
main memory boards be inserted into adjacent slots. The Model 100U card cage has a P2 con-
nector across slots 2, 3, and 4. The processor board is usually inserted in slot 3, with main
memory cards in slots 4 and - possibly - 2.
Sun Workstation cards use the standard Multibus backplane signals, as defined in IEEE stan-
dard 796 for the PI bus. Various Sun cards use the P2 bus in different ways, which may not be
compatible with other vendors' use of this bus. In particular, Sun processor and Sun main
memory cards do not support extended (24-bit) Multibus addressing on the P2 bus. They use
the P2 bus for no-wait-state access to main memory. As a general rule, Sun boards and other
vendors' boards which use the P2 bus should therefore not be installed on the same P2 section.
The signalling conventions used by the various Sun cards on the P2 bus are documented in the
hardware reference manual for each board. For further details, please refer to the appropriate
reference manual.
8.1.3. 100U Card Insertion Order
There are a few restrictions on the placement of cards in the card cage:
• As
stated above, the design of the P2 connector requires that the processor board and
memory boards be inserted in adjacent slots.
• With serial arbitration, bus masters (DMA devices) must be in electrically adjacent slots;
boards which pass the bus arbitration signal through (currently, memory boards and Rev.
C or greater 1/4" tape controller boards) may
be inserted between bus masters.
• In a desktop workstation which includes a disk controller, the disk controller must be below
the processor for proper handling of the serial bus priority. If present, the 1/2-inch tape
controller, a third bus master, must be inserted above the disk controller, because the very
high throughput of the disk controller might otherwise lock out the lower-priority device
for excessive periods:
8-4 Revision H of 12 March 1984