Re: RAMfast to SCSI cable

[harold.h@genie.com (Harold Hislop)]

David Empson shook the bits to their low state when he said:
 
>> With a 50-to-50 ribbon cable, shielding is less important, because
>> every second wire is a ground signal.
 
Very true.
 
>> This is not the case with a 25-to-50 "system" cable.
 
This is subject to debate. IF the cable is made up of 50 conductor
ribbon, and the appropriate ground wires are tied to the appropriate
ground pins on the DB-25 end, then the cable (except right at the
DB-25 itself) is the same as a 50-50 cable.
 
>> I haven't read the part of the SCSI standard on cable specifications,
>> but I would expect that ribbon cables are only supposed to be used for
>> short distances, and only within a shielded enclosure (e.g. a computer
>> orout their 1Kw of RF getting into my
stuff. I run several SCCSI chains, of up to 10', using =only= ribbon
cable (NO shielding added). They are unable to locate any RFI coming from
me, and I am not able to detect any ill effects from their high level of
radiated RF.
 
BTW, the ANSI SCSI specs make intresting reading (esp when one compares
the specs to the SCSI ports that Apple has implemented over the years...
I have yet to find even one such port that met spec... ugh)

--
-Harold
Hardware Coordinator,
Apple II RoundTable, GEnie
SCSI Spoken Here