Seagate Ultra 160, Ultra 320 manual Covered signals, Word Location Signal Meaning

8.3.2.1Covered signals

Table 67 defines the signals to be covered by the protection code and their bit locations in the 21-bit code word. When a SCSI device receives an information byte, it also latches the state of the other SCSI signals and values noted in Table 67.

Table 67: Signals to be covered by the protection code and their bit locations

Code	SCSI
word
location	signal	Meaning
0	DB(0)	Data bit 0 of the information byte
1	DB(1)	Data bit 1 of the information byte
2	DB(2)	Data bit 2 of the information byte
3	DB(3)	Data bit 3 of the information byte
4	DB(4)	Data bit 4 of the information byte
5	DB(5)	Data bit 5 of the information byte
6	DB(6)	Data bit 6 of the information byte
7	DB(7)	Data bit 7 of the information byte
8	DB(8)	Reserved [a]
9	DB(9)	Reserved [a]
10	RSVD	Reserved [b]
11	RSVD	Reserved [b]
12	RSVD	Reserved [b]
13	Seq ID 0	Sequence ID bit 0
14	Seq ID 1	Sequence ID bit 1
15	DB(10)	Redundant bit 0 of the code word
16	DB(11)	Redundant bit 1 of the code word
17	DB(12	Redundant bit 2 of the code word
18	DB(13)	Redundant bit 3 of the code word
19	DB(14)	Redundant bit 4 of the code word
20	DB(15)	Redundant bit 5 of the code word

a.DB(8) and DB(9) are reserved for future use. These signals are negated by the transmitting SCSI device and are ignored by the receiving SCSI device. Both the transmitter and receiver encode these signals in the protection code.

b.For calculation purposes these signals are zero. However, these virtual signals could be used for other functions in a future standard.

The Sequence IDs are encoded in the protection code. A sequence of consecutive information transfers during a Message, Command, or STATUS phase is a run. The Sequence ID increments during a run. A new run begins on every phase change or on each Message Out retry.

Parallel SCSI Interface Product Manual, Rev. A 155