Apple SCSI TermPWR; Was Re: This is funny (ebay)

From: Tothwolf <tothwolf_at_concentric.net>
Date: Sun Feb 24 21:50:43 2002

On Sun, 24 Feb 2002, Richard Erlacher wrote:

> I didn't mean current limiting for the entire supply, but rather just
> for the Termpwr. I'm no longer sure whether it's to be limited to one
> ampere or a half an ampere, or what. I never used to forget once I
> had things written down, and this is specified in the standard.
> Apple probably left out the diode so they wouldn't have to put in the
> fuse. It does cost money, after all. Diodes seem to make pretty
> cheap fuses, too, unless there's no fuse in the circuit, in which case
> they'll hold up until some major component fails. If there's a fuse,
> the diode will, of course, fail first.

The Adaptec AHA-1542B reference manual I have on hand lists available
terminator power current as 800ma. min, and 1.5A max. The AHA-1542C board
I had laying around has a 1.6A fuse, but the newer boards use a
self-resetting surface mount device instead. IIRC, the standard requires
some sort of current limiting device to be present for termpower.

-Toth
Received on Sun Feb 24 2002 - 21:50:43 GMT