Fujitsu MCM3130SS Manuale Utente
SCSI BUS
7-14 C156-E228-02EN
(3) Signal sources
Table 7.6 lists signal sources for each interface phase.
Table 7.6 Bus phases and signal sources
Signal
Bus phase
BSY SEL I/O
C/D
MSG
REQ ACK
DB7-0,
P
ATN TRS
BUS
FREE
N N N N N N N N A
ARBIRATION A W N N N N ID N A
SELECTION I&T I N N N N I I A
RESELECTION I&T T
T
N
N
N
T
I
A
COMMAND T N T T T I I I A
DATA
IN
T N T T T I T I A
DATA
OUT
T N T T T I I I A
STATUS
T N T T T I T I A
MESSAGE
IN T N T T T I T I A
MESSAGE
OUT
T N T T T I I I A
A:
Any SCSI device can drive the signal. Two or more SCSI devices may
drive the signal at the same time.
drive the signal at the same time.
I:
Only the SCSI device which operates as an INIT can drive the signal.
I&T: INIT, TARG, or both can drive this signal according to the interface
sequence.
In the RESELECTION phase, there is a sequence to be driven
simultaneously by both.
In the RESELECTION phase, there is a sequence to be driven
simultaneously by both.
ID: Each SCSI device which is actively arbitrating the bus drives a unique data
bit (SCSI ID). The parity bit may be undriven or driven to the true state, but
must never be driven to the false state.
must never be driven to the false state.
N:
Not to be driven by any SCSI device. The terminator pulls the signal to the
false state.
false state.
T:
Only the SCSI device which operates as an TARG can drive the signal.
W:
Only one SCSI device which wins ARBITRATION can drive the signal.