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Ground
1
2
- Data Bit 0 (DBO)
4
"
1
6
"
2
8
"
3
10
"
4
12
"
5
14
"
6
16
- Data Bit 7 (DB7 )
18
- Data Bit P (DBP)
20
Ground
23
22
Ground
25
24
Ground
27
26
No connection
28
Ground
30
Ground
32
- Attention
34
Ground
36
- Busy
38
- Acknowledge
40
- Reset
42
- Message
44
- Select
46
- Control/Data
48
- Request
49
50
- Input/Output
Figure 4-2.
SCSI Bus Pin Assignments
4.2
MESSAGE SPECIFICATION
The message system allows communication between an Initiator and
an ACB-5500 for purposes of physical path management.
This
section defines the messages supported by the ACB-5500.
4.2.1
MESSAGE SYSTEM,
The ACB-5500 supports a considerable number of messages to
perform such special
functions
as disconnect/reconnect
and
command linking.
Certain Initiators, including the Adaptec
host
adapters, fully support those messages, but certain others do
not.
The Initiator indicates that it can support more than the
COMMAND COMPLETE message by creating the ATTENTION condition
prior to the bus state of SEL asserted and BSY deasserted in the
SELECTION phase.
If the ACB-5500 sees this ATTENTION condition, it will request a
message byte
from
Initiator by executing
a
MESSAGE
OUT
information transfer.
The outcoming IDENTIFY message indicates
the drive to be selected and also
indicates whether
the
disconnect/reconnect functions are supported by the Initiator.
500504-00
4-12
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