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Re: RAMfast to SCSI cable
In article <4acd19$l9o@newsbf02.news.aol.com>,
RUBYWAND <rubywand@aol.com> wrote:
> In article <DJ9rpL.CM0@actrix.gen.nz>, dempson@atlantis.actrix.gen.nz
> (David Empson) writes:
> >
> >If you make any mistakes with a SCSI cable, you are likely to damage
> >the SCSI card as well as the drive mechanism (a friend of mine managed
> >to blow up a SCSI mechanism by plugging a cable in upside down).
>
> When the CD-ROM unit arrived w/o a cable, an order was placed right
> away ($9.95 + postage). Then, it occurred to me that such a cable might
> be pretty simple to make. IF Sequential designed their 25-pin connection
> for a convenient ribbon cable match to the 50-pin SCSI plug, then
> alternating lines might go to top and bottom SCSI pins starting from one
> end of the plug.
Definitely not. The RAMFast should use the same pinout as the Mac and
Apple's own SCSI cards. The cable pinout is documented in the
technical reference manual for the Apple High-Speed SCSI card
(and the original one as well).
This pinout is not a simple mapping from one end to the other.
I repeat that it is NOT easy to make one of these yourself. Apart from
any issues of wiring errors, you also need a properly shielded cable
to minimise noise being picked up or radiated. You should definitely
not use a ribbon cable.
Here is the pinout, assuming I haven't made any typos (I can't see any).
DB-25 50-pin Function
1 49 -REQ
2 46 -MSG
3 50 -I/O
4 45 -RST
5 44 -ACK
6 43 -BSY
7 16,18,19 Ground lines
8 26 -DB0
9 20,21,22 Ground lines
10 29 -DB3
11 31 -DB5
12 32 -DB6
13 33 -DB7
14 1,2,3 Ground lines
15 48 -C/D
16 4,5,6 Ground lines
17 41 -ATN
18 7,8,9,11 Ground lines
19 47 -SEL
20 34 -DBP
21 27 -DB1
22 28 -DB2
23 30 -DB4
24 23,24,25 Ground lines
25 38 TERMPWR
The unlisted pins in the 50-pin connector (10, 12, 13, 14, 15, 17, 35,
36, 37, 39, 40, 42) are ground.
Note: the numbers for the 50-pin connector are counted along each row,
like a DB-25. They are NOT the wire numbers in a ribbon cable.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand