Avago Technologies LSI53C895A - Manual (Page 65)

SCSI Functional Description 2-39
Figure 2.6 Regulated Termination for Ultra2 SCSI
2.2.14 Select/Reselect During Selection/Reselection
In multithreaded SCSI I/O environments, it is not uncommon to be
selected or reselected while trying to perform selection/reselection. This
situation may occur when a SCSI controller (operating in the initiator
mode) tries to select a target and is reselected by another. The Select
SCRIPTS instruction has an alternate address to which the SCRIPTS will
jump when this situation occurs. The analogous situation for target
devices is being selected while trying to perform a reselection.
Once a change in operating mode occurs, the initiator SCRIPTS should
start with a Set Initiator instruction or the target SCRIPTS should start
with a Set Target instruction. The Selection and Reselection Enable bits
(
SCSI Chip ID (SCID) bits 5 and 6, respectively) should both be asserted
so that the LSI53C895A may respond as an initiator or as a target. If only
selection is enabled, the LSI53C895A cannot be reselected as an
initiator. There are also status and interrupt bits in the
SCSI Interrupt
UCC5630
4
5
6
7
11
12
13
14
15
16
17
LINE1+
LINE1
−
LINE2+
LINE2
−
LINE3+
LINE3
−
LINE4+
LINE4
−
LINE5+
LINE5
−
DISCNCT
32
31
30
29
25
24
23
22
33
34
35
20
21
LINE9
−
LINE9+
LINE8
−
LINE8+
LINE7
−
LINE7+
LINE6
−
LINE6+
SE
LVD
HVD
DIFFSENSE
DIFF B
SDP0
−
SDP0+
SD7
−
SD7+
SD6
−
SD6+
SD5
−
SD5+
To LED
Drivers
SD0+
SD0
−
SD1+
SD1
−
SD2+
SD2
−
SD3+
SD3
−
SD4+
SD4
−
22 K
0.1
µ
f
DIFFSENSE connects to the SCSI bus Diffsense line to detect what type of devices (SE,
LVD, or HVD) are connected to the SCSI bus. DISCNCT shuts down the terminator when
it is not at the end of the bus. The disconnect pin low enables the terminator. Use
additional UCC5630 terminators to terminate the SCSI control signals and wide SCSI
data byte as needed.