Mike Harrison wrote:
>
> On Mon, 7 Sep 1998 11:27:00 PDT, you wrote:
>
> >Steve Smith wrote:
> >
> >both the SDA (data line) and SCL (clock) should be open drain.
> Wrong - only SDA needs to be open drain unless you are using a
> multi-master system.

Nope, Steve is right.
SCL _does_ have to be open drain.
Or open-drain simulated as per Tjaart's mail.

I2C devices are able to insert wait states by holding SCL low
with their open drain outputs.

If a master is driving the clock with a normal totem-pole output,
you'll get a conflict of course.

Some naughty programmers get away with it because the slave I2C
devices are so fast they never need to hold SCL low.
Their sins can catch up with them when they need
to add a slow slave device that does!

It's not hard to do it right in the first place.
Knowingly doing it the wrong way is inexcusable! :-)