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From: biswa@janus.Berkeley.EDU (Biswa Ghosh)
Newsgroups: comp.sys.mac.hardware
Subject: Help: SID-II Question
Message-ID: <40125@ucbvax.BERKELEY.EDU>
Date: 21 Dec 90 06:59:45 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: biswa@janus.Berkeley.EDU (Biswa Ghosh)
Organization: University of California, Berkeley
Lines: 24

Hi Folks,

Believe it or not, I *finally* got around to assembling by sid-ii device.
And, it doesn't work. Aack!

I've found the following problem, and it seems to be with the modem/printer
ports on my SE/30. The sid is parasitically powered from the TXD+ and TXD-
outputs on the ports (pins 8 and 5 respectively). They are supposed to be
differential outputs, so that when one is positive, the other is negative.

Problem is, they are both sitting at +2.7V all the time, so my sid only
gets a 2.7V supply. How can I get the outputs to be differential, so that
the sid can get the +5V that it needs?

I made the measurements both with and without the sid connected, with nothing
connected to the other port, and the result is the same on both ports (i.e.,
txd+ and txd- are both positive).

Any ideas?

Biswa Ghosh
550 Cory Hall				arpa: biswa@janus.berkeley.edu
U.C. Berkeley				uucp: ...ucbvax!janus!biswa
Berkeley, CA 94720			tel:  (415) 642-0395