Seagate Ultra 320 - Manual (Page 32)

18 Parallel SCSI Interface Product Manual, Rev. A )
Figure 3. Voltage and current definitions
Figure 4 defines the signaling sense of the voltages appearing on the – signal and + signal lines as follows:
a. The – signal terminal of the driver shall be negative with respect to the + signal terminal for an asserted
state.
b. The – signal terminal of the driver shall be positive with respect to the + signal terminal for a negated state.
Figure 4. LVD Signaling sense
Note. For a description of V
BIAS
see Section 7.3.1 of ANSI specification (SPI-5), T10/1525D.
2.3 OR-tied signals
The BSY, SEL, and RST signals shall be OR-tied. BSY and RST signals may be simultaneously driven true by
several SCSI devices. No signals other than BSY, SEL, RST, DB(P_CRCA), and DB(P1) are simultaneously
driven by two or more SCSI devices. DB(P_CRCA) and DB(P1) shall not be driven false during the ARBITRA-
TION PHASE but may be driven false in other phases.
+ SIGNAL
I–
– SIGNAL
– TRANSCEIVER
I+
Vs
V–
V+
LOGICAL 1
(ASSERTED)
(TRUE)
LOGICAL 0
(NEGATED)
(FALSE)
TIME
DIFFERENTIAL B
US
V
O
LT
A
G
E
V
CM
=(V
+
+V
–
)/2 V
CM
V
N
V
+
V
–
V
–
–V
+
V
A
V
BIAS
0V (OFF)
LOGICAL 1
(ASSERTED)
(TRUE)