IBM 7133 Series, Service Manual

Page: 52 / 230

|
SSA Bypass Cards (Models 020 and 600)
| The four bypass cards that are at the back of the 7133 Models 020 and 600 provide the
| connections between the external SSA cables and the disk drive module strings. Each
| bypass card has two external SSA connectors. Through these connectors, the bypass
| cards and, therefore, the disk drive module strings, can be connected to each other or to
| the using system.
| The bypass cards can operate in Bypass mode or in Forced Inline mode. The mode can
| be changed by swapping the positions of the jumpers (see “Bypass Card Jumpers” on
| page 1-40).
| Note: The cards need not all be in the same mode.
|
Bypass Mode
| When a bypass card is jumpered to operate in Bypass mode, it monitors both of its
| external connectors. If it detects that one of its connectors is connected to a powered-on
| SSA adapter or device, it switches to Inline state; that is, it connects the internal SSA links
| to the external connector.
| If the bypass card detects that neither of its connectors is connected to a powered-on SSA
| adapter or device, it switches into Bypass state; that is, it connects the internal strings
| together, and disconnects them from the external connectors. Therefore, when a 7133
| that has all its bypass cards jumpered for Bypass mode is not connected externally, all 16
| disk drive module slots are connected in one internal SSA loop.
| In the following diagrams, two strings of four disk drive modules in a 7133 Model 020 or
| 600 are connected to two SSA adapters. If power is on at both adapters, the loop is
| connected as shown here:
A d a p te r 1 A da p ter 2
D is k
16
D is k
15
D is k
14
D is k
13
D is k
12
D is k
11
D is k
10
D is k
9
16 4 5 9 8 1 13 12
D is k
1
D is k
2
D is k
3
D is k
4
D is k
5
D is k
6
D is k
7
D is k
8
A B A B
1-38
7133 Service Guide