David Blain <dblain@MEDIAONE.NET> wrote:
> This is what I am looking for to put in the Unknown box... it needs to
> disconnect the non-selected SX, as well as, disable/disconnect the
> Oscillator when there is 12v on the ISP's osc1 pin.

What you need is either mechanical jumpers or switches (easiest), or
low-resistance analog switches that can handle a 0-13V range.  Typical analog
switches would require a supply voltage greater than the voltage to be
switches; running the analog switch on 15V would do the trick.  The old
metal-gate CMOS parts such as the 4066 were rated for 15V operation.  Note
that if you run them on 15V, the control inputs also have to swing from 0 to
15V, so you won't be able to directly control them from a normal CMOS level.
There are probably newer, fancier analog switches from Maxim, Linear Tech,
etc. that are better suited (and lower resistance).

> I am not sure if I need to disconnect the oscillator or just set it's O/E to
> LOW.  This is a quote from Digikey's catalog regarding this oscillator:
>
>   "Tri-State Logic uses the two standard logic levels of
>   high (logic 1) and low (logic 0) but has added a
>   third state that is not a logic level but an open
>   circuit condition that effectively disconnects the

Unless otherwise explicitly stated in the specifications, tri-state outputs
still may not be connected to voltages more than a few tenths of a volt
below ground or above the positive supply.