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How to connect a 25 PIN scanner SCSI connector (DB25) to a common 8 bit SCSI
connector.
|
Signal |
Pin # |
Cable
Conductor
# |
Pin # |
Cable conductor # |
Signal |
|
Set 2 |
Set 1 |
Set 1 |
Set 2 |
DB25 |
Flat cable to
DB 25 |
|
SIGNAL RETURN |
1 |
1 |
1 |
2 |
2 |
26 |
8 |
15 |
-DB(0) |
|
SIGNAL RETURN |
2 |
3 |
3 |
4 |
4 |
27 |
21 |
16 |
-DB(1) |
|
SIGNAL RETURN |
3 |
5 |
5 |
6 |
6 |
28 |
22 |
18 |
-DB(2) |
|
SIGNAL RETURN |
4 |
7 |
7 |
8 |
8 |
29 |
10 |
19 |
-DB(3) |
|
SIGNAL RETURN |
5 |
9 |
9 |
10 |
10 |
30 |
23 |
20 |
-DB(4) |
|
SIGNAL RETURN |
6 |
11 |
11 |
12 |
12 |
31 |
11 |
21 |
-DB(5) |
|
SIGNAL RETURN |
7 |
13 |
13 |
14 |
14 |
32 |
12 |
23 |
-DB(6) |
|
SIGNAL RETURN |
8 |
15 |
15 |
16 |
16 |
33 |
13 |
25 |
-DB(7) |
|
SIGNAL RETURN |
9 |
17 |
17 |
18 |
18 |
34 |
20 |
14 |
-P_CRCA |
|
GROUND |
10 |
19 |
19 |
20 |
20 |
35 |
7 |
13, 22 |
GROUND |
|
GROUND |
11 |
21 |
21 |
22 |
22 |
36 |
9 |
17 |
GROUND |
|
(reserved) |
12 |
23 |
23 |
24 |
24 |
37 |
14 |
2 |
(reserved) |
|
(no connection) |
13 |
25 |
25 |
26 |
26 |
38 |
25 |
24 |
TERMPWR |
|
(reserved) |
14 |
27 |
27 |
28 |
28 |
39 |
16 |
6 |
(reserved) |
|
GROUND |
15 |
29 |
29 |
30 |
30 |
40 |
18 |
10 |
GROUND |
|
SIGNAL RETURN |
16 |
31 |
31 |
32 |
32 |
41 |
17 |
8 |
-ATN |
|
GROUND |
17 |
33 |
33 |
34 |
34 |
42 |
24 |
22 |
GROUND |
|
SIGNAL RETURN |
18 |
35 |
35 |
36 |
36 |
43 |
6 |
11 |
-BSY |
|
SIGNAL RETURN |
19 |
37 |
37 |
38 |
38 |
44 |
5 |
9 |
-ACK |
|
SIGNAL RETURN |
20 |
39 |
39 |
40 |
40 |
45 |
4 |
7 |
-RST |
|
SIGNAL RETURN |
21 |
41 |
41 |
42 |
42 |
46 |
2 |
3 |
-MSG |
|
SIGNAL RETURN |
22 |
43 |
43 |
44 |
44 |
47 |
19 |
12 |
-SEL |
|
SIGNAL RETURN |
23 |
45 |
45 |
46 |
46 |
48 |
15 |
4 |
-C/D |
|
SIGNAL RETURN |
24 |
47 |
47 |
48 |
48 |
49 |
1 |
1 |
-REQ |
|
SIGNAL RETURN |
25 |
49 |
49 |
50 |
50 |
50 |
3 |
5 |
-I/O |
Note: "-P_CRCA" was "-DB(P0)" (parity zero)
before the introduction of CRC.
The table is double-width to prevent its length from getting excessive, and is
"mirror-imaged" to make the data easier to understand and to
show how the wires are "paired" for the 50 pins systems. Notice:
The cheap 25 pin DB25 SCSI connectors, used for Apple and scanners are NOT
"paired".
On the outside are the signal names. Notice
that all the "real signals" are on the right-hand side, and the "signal returns"
and grounds are on the left. The middle left two columns show the conductor numbers
assigned to each signal; these are the numbers of the wires in the cable. The
numbers between those two columns and the signal names represent two different
sets of pin number assignments, which are used for different connector types in
the SCSI standards.
"Set 1" is the same as the conductor numbering; since the
numbers alternate, this means that consecutive numbers are "pairs"; #1 and #2,
#3 and #4 and so on, to #49 and #50. "Set 2" instead numbers going down the left
column and then does the right column. The DB25coluns represent is the the
25 pin scanner or Apple (R) connector.
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Connector Alternative
|
External Cables
|
Internal Cables
|
|
Connector Type
|
Pin Set Number
|
Connector Type
|
Pin Set Number
|
|
"Alternative 1"
|
High Density
|
2
|
High Density
|
2
|
|
"Alternative 2"
|
Centronics
|
1
|
Regular Density
|
1
|
This means that the older cable styles--Centronics for external and regular
density for internal--have the pin numbers the same as the conductor numbers.
Cables using the newer, high density connectors--for both internal and external
cables--use the different numbering specified as "Set 2".
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