chris@com50.c2s.mn.org (Chris Johnson) (05/26/90)
Here's the standard single-ended SCSI cable pin assignments for
a non-shielded connector:
SIGNAL PIN NUMBER
------ ----------
-DB(0) 2
-DB(1) 4
-DB(2) 6
-DB(3) 8
-DB(4) 10
-DB(5) 12
-DB(6) 14
-DB(7) 16
-DB(P) 18
GROUND 20
GROUND 22
GROUND 24
TERMPWR 26
GROUND 28
GROUND 30
-ATN 32
GROUND 34
-BSY 36
-ACK 38
-RST 40
-MSG 42
-SEL 44
-C/D 46
-REQ 48
-I/O 50
All odd pins except pin 25 are connected to ground.
Pin 25 is left open.
In fact, Pin 25 MUST be left unconnected, because if
the connector were plugged in upside down and Pin 25
were grounded, you'd short terminator power to ground.
And then the smoke escapes.
I'd suggest not scrimping on connecting the odd pin
grounds because single-ended SCSI is plenty sensitive
to noise even with all the grounding. But I'm not an
expert in the area of analog/interference electronics
or signal skew or any other fun real-world transmission
media problems. You're mileage will vary.
--
...Chris Johnson chris@c2s.mn.org ..bungia!com50!chris
Com Squared Systems, Inc. St. Paul, MN USA +1 612 452 9522hyc@math.lsa.umich.edu (Howard Chu) (05/30/90)
In article <3471@rodan.acs.syr.edu> jfbruno@rodan.acs.syr.edu (John Bruno) writes: >I have just purchased a SCSI host adapter for my machine (an Atari 1040ST) and >the SCSI out on the board has a connector that I assume is a standard SCSI >connector (if there is such a thing), it looks like this: > > 1 49 > . . . . . . . . . . . . . . . . . . . . . . . . . > . . . . . . . . . . . . . . . . . . . . . . . . . > 2 50 On a standard 50-pin SCSI cable, just about every other line is just a ground. On the 25-pin Mac cable, you basically omit the extra ground lines. (And hope you don't fall prey to too much noise as a result... }-) The Supra host adapter for the ST comes with docs including the pinout of the 25-pin cable. I think it's distributable... -- -- Howard Chu @ University of Michigan ... the glass is always greener on the side ...