Originally Posted By: mlord
The SMC ethernet chip has a spare TTL-output pin (as well as a spare input), which could be wired to pin-8 of the ds1821 temperature sensor chip. Then the pull-down to GND, and subsequent pull-up to Vdd could be accomplished automatically by Hijack.

Just a simple pin-lift + jumper wire. And it could be left in place permanently.

This one is still nagging at me. I'd like to make the sensor fix simple enough that just about anyone here could do it easily, with modest soldering skills. It's not bad right now, but does require the special Hijack load and a somewhat timely manual switch toggle.

If we used the spare output from the ethernet chip, then just a pin lift and jumper would be needed, and the rest could be stock and automatic. But then.. anyone who can accomplish the pin lift, could probably handle the existing procedure too.

So.. about that ethernet chip..

The SMC LAN91C96 chip actually has several spare in/out pins. They're not "GPIO", in the sense that they are fixed as either inputs or outputs. But they are there, and unused.

Pins 96,97,99 are IOS0,IOS1,IOS2 --> general purpose TTL input pins, which Patrick was kind enough to factory equip with 10K pull-ups and pads for an unpopulated pin header ("PL9" pins 1-3, plus GND on pin 4).

Pin 3 is also a general purpose TTL input pin, with an internal pull-down (floats to zero on no-connect).

Pins 2,4 are general purpose TTL outputs (capable of 2mA source, or 4mA sink).

Those are all accessible through the ethernet chip's internal registers.
So.. I wonder what other good uses they might have ?