Fujitsu MBA3073 SERIES Technical Manual page 24

(2) BSY (BUSY)
The BSY signal indicates that the SCSI bus is in use. In the ARBITRATION phase, this signal is
used to request for the bus usage priority.
(3) SEL (SELECT)
The SEL signal is used by the INIT to select a TARG (in the SELECTION phase) or by the
TARG to reselect an INIT (in the RESELECTION phase).
(4) C/D (CONTROL/DATA)
This is a combination of I/O and MSG signals, and specifies a type of information transferred on
the data bus. The C/D signal is always driven by the TARG (see Table 1.1).
(5) I/O (INPUT/OUTPUT)
The I/O signal specifies the information transmission direction on the data bus. It is also used to
identify the SELECTION phase or RESELECTION phase. This signal is always driven by the
TARG (see Table 1.1).
(6) MSG (MESSAGE)
A signal sourced by a target to indicate the MESSAGE phase or a DT DATA phase depending on
whether C/D is true or false. Asserted indicates MESSAGE or DT DATA (see Table 1.1).
Table 1.1
Signal
C/D MSG I/O
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
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INFORMATION TRANSFER phase identification
Phase
ST DATA OUT INIT -> TARG
ST DATA IN INIT <- TARG
DT DATA OUT INIT -> TARG
DT DATA IN INIT <- TARG
COMMAND INIT -> TARG
STATUS INIT <- TARG
MESSAGE OUT INIT -> TARG
MESSAGE IN INIT <- TARG
Direction
ST Data phase
DT Data phase
MESSAGE
Comment
Data phase
C141-C015