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

Page: 26 / 224

2–2 Theory of Operation
2.2 SF3x Series Storage Enclosure
The SF3x storage enclosure exists with either two, six, or twelve half-
height, 3-1/2 inch disk ISEs. The ISEs are arranged on two DSSI buses;
one for up to six ISEs in the front of the enclosure and one for up to six
ISEs in the rear of the enclosure. These can be further divided up into
four DSSI buses by splitting each bus into left and right sides.
Each ISE slides into a slot in the enclosure, where it plugs directly into a
backplane. There is one backplane for the front ISEs and one for the rear
ISEs.
2.2.1 DSSI Node ID
Each slot in the backplane is assigned a letter designation, from A
through F. Each slot has a corresponding factory-designated DSSI node
ID (Table 2–1). These DSSI node IDs are the same for both front and rear
slots in the SF3x storage enclosure.
Table 2–1 SF3x Factory-set DSSI Node IDs
Position Backplane Location DSSI Node ID
A upper left slot 0
B upper right slot 1
C middle left slot 2
D middle right slot 3
E lower left slot 4
F lower right slot 5
You can change the DSSI node ID for an ISE in any given slot position by
using DIP switches provided on the SF3x enclosure’s transition module.
Figure 2–1 shows the location of the switches for each slot position.
Table 2–2 shows what the switches must be set to for each slot position.