[rescue] Re: The onyx godness

James Lockwood james at foonly.com
Fri Jan 10 09:51:17 CST 2003

On Fri, 10 Jan 2003, Scott Newell wrote:

> Aren't they voltages TTL level, not RS-232?

Yes, though they can tolerate some reverse voltage.  Running your port as
RS-423 with an inline diode (again, see the doubleX docs) solves this
problem while still giving you well over the minimum TTL voltage (2.2V).

> I've been thinking for some time it would be handy to enable the mouse and
> keyboard ports as generic serial ports under OpenBSD, so that I could
> quickly interface to embedded projects (such as the webpal and recent GPS
> modules) that speak TTL level '232 without having to tie on a MAX232.

Just about all of the GPS modules I've seen can handle RS-423 swings.  You
might want to try this first.  Though it's stretching the specs (and any
vendor that supplies "TTL" level serial interfaces should be strung up
by their own serial cables) both -423 and -232D require a +ve threshold
for SPACE and _most_ TTL 0 outputs will come in under it.  Maybe.

This is assuming, of course, that they map TTL 0 to MARK and TTL 1 to
SPACE.  If they don't then you'd need an inverter, and at that point you
might as well just use a MAX232.  That's what I'd recommend.

The mouse and keyboard should already be implemented as generic serial
ports.  You'd just be accessing them with your own app instead of, say,
an X server.


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