Digital Equipment EK-SFXXS-SG-003, Service Manual

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2–14 Theory of Operation
2.3 SF7x Series Storage Enclosure
The SF7x storage enclosure connects its resident disk ISEs to the DSSI
bus in parallel. If one of the four drive positions is empty, that position
is ignored. If a position is occupied, the ISE can be on-line or off-line,
MSCP enabled or disabled, powered up or down, or failed. In any case,
the performance of the DSSI bus is not directly affected.
The storage enclosure provides termination power for the DSSI bus when
operating in either split-bus mode or through-bus mode.
2.3.1 DSSI Node ID
Four switchpacks behind the OCP door are used for setting the DSSI node
ID of the ISEs in the SF7x enclosure (Figure 2–5). The leftmost switch is
the MSCP enable switch, and must be set in the down position in order
for MSCP to be enabled. The other switches are used to set the DSSI
node ID, where the rightmost switch is the least significant.
Typical switch settings are shown in Table 2–5 and Table 2–6.
Table 2–5 DSSI ID Switch Settings (DSSI VAXcluster)
Disk ISE
DSSI
ID Setting
1
Positions 1, 2, 3, 4, 7 and 8
Left Rear (LR)
Left Front (LF)
Right Front (RF)
Right Rear (RR)
1
2
3
4
001
010
011
100
1
‘‘0’’ = down, ‘‘1’’ = up.