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108 Parallel SCSI Interface Product Manual, Rev. A
A SCSI target port shall respond to an attention condition with MESSAGE OUT phase as follows:
a. If an attention condition is created during a COMMAND phase, the target shall enter MESSAGE OUT
phase after transferring part or all of the command descriptor block.
b. If an attention condition is created during a DATA phase, the target shall enter MESSAGE OUT phase at
the target's earliest convenience (for example, on a logical block boundary). The initiator shall continue
REQ/ACK handshakes until it detects the phase change.
c. If an attention condition is created during a STATUS phase, the target shall enter MESSAGE OUT
phase after the status byte has been acknowledged by the initiator.
d. If an attention condition is created during a MESSAGE IN phase, the target shall enter MESSAGE OUT
phase before it sends another message. This permits a MESSAGE PARITY ERROR message from the
initiator to be associated with the appropriate message.
e. If an attention condition is created during a SELECTION phase, the target shall enter MESSAGE OUT
phase after that SELECTION phase.
f. If SPI (SCSI Parallel Interface) information unit transfers are disabled and an attention condition is
detected during a RESELECTION phase, the SCSI target port shall enter MESSAGE OUT phase after
the SCSI target has sent its IDENTIFY message for that RESELECTION phase.
g. If an attention condition is created during a RESELECTION phase the target shall enter MESSAGE
OUT phase after the target has sent the first Information Transfer phase.
h. If the attention condition is detected during the transfer of a SPI data stream information unit, the target
shall terminate the current stream by entering into MESSAGE OUT phase at the end of any SPI data
stream information unit in the current stream.
i. If the attention condition is detected between SPI information units, the target shall enter MESSAGE
OUT phase at the completion of the next SPI information unit.
During a RESELECTION phase, the initiator should only create an attention condition to transmit an ABORT
TASK SET, Abort Task, Target Reset, Clear Task Set, Disconnect, Logical Unit Reset, or NO OPERATION
message. Other uses may result in ambiguities concerning the nexus.
The initiator shall keep the ATN signal asserted throughout the MESSAGE OUT phase if more than one byte is
to be transferred. Unless otherwise specified, the initiator may negate the ATN signal at any time that does not
violate the specified setup and hold times, except it shall not negate the ATN signal while the ACK signal is
asserted during a MESSAGE OUT phase. Normally, the initiator negates the ATN signal while the REQ signal
is true and the ACK signal is false during the last REQ/ACK handshake of the MESSAGE OUT phase.
5.2 Bus reset condition
The bus reset condition is used to create a hard reset (see Section 5.3) for all SCSI devices on the bus and
change the bus to a BUS FREE phase. This condition shall take precedence over all other phases and condi-
tions. Any SCSI device may create the bus reset condition by asserting the RST signal for a minimum of a
reset hold time.
Environmental conditions (for example, static discharge) may generate brief glitches on the RST signal. SCSI
devices shall not react to glitches on the RST signal that are less than a reset delay. The manner of rejecting
glitches is vendor-specific. The bus clear delay following a RST signal transition to true is measured from the
original transition of the RST signal. This limits the time to confirm the RST signal to a maximum of a bus clear
delay.
5.3 Hard reset
A SCSI device detecting a reset event shall release all SCSI bus signals within a bus clear delay of the transi-
tion of the RST signal to true, except the RST signal if it is asserting RST. The BUS FREE phase always fol-
lows the hard reset condition. The SCSI device shall not assert the RST signal in response to a reset event on
the same bus segment.
- Parallel SCSI Interface 1
- Revision status summary sheet 5
- Table of Contents 7
- List of Figures 13
- 1.0 Interface requirements 15
- standards 16
- 1.4 Summary of SCSI messages 26
- 2.0 SCSI bus 27
- 2.1 SCSI bus signals overview 29
- 2.2 Signal states 31
- 2.3 OR-tied signals 32
- 2.4 Signal sources 33
- 2.5 SCSI bus timing 34
- 0 0.5 0 0.2 39
- induced time asymmetry 39
- due to resis 43
- 2.6 Measurement points 47
- 2.9 Data transfer modes 51
- 2.12 Negotiation 53
- PPR, SDTR Less than or equal 55
- 2.12.4 Transfer agreements 56
- Table 13: Transfer agreements 56
- bit shall be set to zero 61
- Transfer 62
- 3.0 Logical characteristics 65
- 3.2 SELECTION phase 69
- 3.3 RESELECTION phase 72
- 3.4 SCSI bus fairness 73
- 3.6 COMMAND phase 89
- 3.7 DATA phase 89
- 3.8 STATUS phase 90
- 3.9 MESSAGE phase 90
- 3.11 SCSI bus phase sequences 92
- 3.12 Data bus protection 95
- 4.2 Message formats 97
- 4.3 Message categories 99
- 7 6 5 4 3 2 1 0 101
- 0 IDENTIFY DISCPRIV LUN 101
- Target’s Parallel Protocol 109
- 4.4 Task attribute messages 116
- 4.5 Task management messages 119
- 5.1 Attention condition 121
- 5.2 Bus reset condition 122
- 5.3 Hard reset 122
- 5.4 Reset events 123
- 6.0 SPI information units 127
- [3] See Figure 16 129
- [4] See Figure 18 129
- [3] See Figure 18 130
- 6.2 SPI information units 132
- field shall be reserved 135
- field is not zero 135
- 129 143
- 7.0 SCSI commands 145
- See notes following Table 61 148
- 7.3 Status 152
- 7.4 Command examples 154
- 7.5 Timing examples 156
- 7.8 Parameter rounding 163
- 8.0 Drive features 165
- Command, Message, and Status 168
- (Bits 14 171
- Seagate Technology LLC 186
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