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7.6 Bus Phases
C156-E228-02EN 7-37
Unless a parity error is detected, the TARG can execute the received message
immediately after its reception. If a parity error is detected, the TARG ignores
that part of the message which has been received after the detection of the parity
error. Suppose that when the INIT retransmits a series of messages in the
MESSAGE OUT phase, the TARG has already executed some messages. In this
event, the TARG must handle the received messages so that no logical
contradiction will occur (for example, the TARG must ignore received messages
that have already been executed).
If the TARG receives all message information normally without detecting a parity
error, the TARG must enter an INFORMATION TRANSFER phase other than a
MESSAGE OUT phase and must send at least one byte of information in order to
advise the INIT that message transfer retry is unnecessary. However, for some
types of message (ABORT and BUS DEVICE RESET, for example), the TARG
can report the normal completion of message reception by entering a BUS FREE
phase.
7.6.10 Signal requirements concerning transition between bus phases
When the SCSI bus is at a midpoint between two INFORMATION TRANSFER
phases (during the period of bus phase transition), interface signals must satisfy
the requirements below.
1) The status of the BSY, SEL, REQ, and ACK signals must not change.
2) The status of the ATN and RST signals can change within the range
determined by the ATTENTION condition (see Subsection 7.7.1) or RESET
condition (see Subsection 7.7.2).
3) The status of the C/D, I/O and MSG signals and the DATA BUS (DBn) can
change. However, the direction of data transfer over the DATA BUS must
satisfy the following rule. (See Figure 7.18.)
• When changing the direction of transfer from Out (from INIT to TARG) to In
(from TARG to INIT), the TARG must begin to drive the data bus (DBn) at
least Data Release Delay + Bus Settle Delay after making the I/O signal true.
The INIT must stop driving the data bus within Data Release Delay after the
I/O signal becomes true.
• When changing the direction of transfer from In (from TARG to INIT) to Out
(from INIT to TARG), the TARG must stop driving the data bus (DBn)
within Deskew Delay after making the I/O signal false.