7.6 Bus Phases
C156-E228-02EN 7-19
Bus Clear Delay (Max)
B
us Settle Delay +
Bus Clear Delay (Max)
Bus Settle Delay (Min)
Figure 7.9 BUS FREE phase
Transition to a BUS FREE phase occurs when the TARG stops the BSY signal in
one of the following events:
• When the RESET condition has been detected
• When the TARG has received ABORT message
• When the TARG has received a BUS DEVICE RESET message
• When the TARG has sent a DISCONNECT message normally
• When the TARG has sent a COMMAND COMPLETE message normally
If a SELECTION or RESELECTION phase is terminated unsuccessfully, the
SCSI bus enters a BUS FREE phase. This BUS FREE phase is generated when
the SEL signal becomes false.
In cases other than the above, if the TARG negates the BSY signal to enter a BUS
FREE phase, the TARG informs the INIT that it has detected an ERROR
condition on the SCSI bus. The TARG can enter a BUS FREE phase forcibly
regardless of the ATN signal status; the INIT must treat that phase transition as
indicating abnormal end of a command. The TARG clears all retained data or
status and terminates the command being executed. It can then create sense data
indicating the detailed error condition. If the INIT detects a BUS FREE phase
when it is not expected, it should issue a REQUEST SENSE command to read the
sense data.