7.2 Interface Signal Definition
(3) SEL (SELECT)
This signal is used by an INIT to select a TARG (SELECTION phase) or by a TARG to reselect an INIT (RESELECTION phase).
(4) C/D (CONTROL/DATA)
This signal is driven by a TARG to identify the type of information transferred on the DATA BUS in combination of I/O and MSG signals. (See Table 7.1)
(5) I/O (INPUT/OUTPUT)
This signal is driven by a TARG to specify the information transfer direction on the DATA BUS or to identify a SELECTION or RESELECTION phase. (See Table 7.1)
(6) MSG (MESSAGE)
This signal is driven by a TARG to indicate that a message is being transferred on the DATA BUS. (See Table 7.1)
(7) REQ (REQUEST)
This signal is driven by a TARG to indicate a transfer request to an INIT in
INFORMATION TRANSFER phase.
(8) ACK (ACKNOWLEDGE)
This signal is driven by an INIT to indicate a response for REQ signal to a TARG in the INFORMATION TRANSFER phase.
(9) ATN (ATTENTION)
This signal is driven by an INIT to indicate that the INIT has a message to be transferred to the TARG and is used to generate an ATTENTION condition.
(10) RST (RESET)
This signal indicates the RESET condition which is used to clear all SCSI devices on the bus.
Table 7.1 INFORMATION TRANSFER phase identification
C/D | I/O | MSG | Direction | Phase | ||
|
|
|
|
|
|
|
0 | 0 | 0 | Data | INIT → | TARG | DATA OUT |
0 | 1 | 0 | Data | INIT ← | TARG | DATA IN |
1 | 0 | 0 | Command (CDB) | INIT → | TARG | COMMAND |
1 | 1 | 0 | Status | INIT ← | TARG | STATUS |
0 | 0 | 1 | – | – |
| not used |
0 | 1 | 1 | – | – |
| not used |
1 | 0 | 1 | Message | INIT → | TARG | MESSAGE OUT |
1 | 1 | 1 | Message | INIT ← | TARG | MESSAGE IN |
