There is a line in the Parameters table on p.1 of the datasheet, which describes the function of the Tri-state. It's a kind of an enable-disable pin. • If Tri-state pin is logic "1", then oscillator is connected to the output pin. Same happens if Tri-state is left unconnected (there's probably an internal pull-up). • If Tri-state pin is logic "0", then oscillator is not connected to the output pin, and output is floating. The fact that it's floating may be useful if you need to switch between several clock sources. You would enable one of them, and Tri-state the others to prevent contention between multiple outputs. edit: Here's an example where an enable/disable with tri-state is used with an external clock source. When connecting external clock source to J1, the J2 jumper should be installed. The resistor R1 protects from a direct short between clock outputs. (schematic from p.22 in this user guide and datasheet for that oscillator)

You are correct - leaving it open will enable the oscillator. One way of covering your bases is to put a resistor in your PCB but don't stuff it if not needed. In this case, it would be between the tri-state pin and the positive power supply. Putting such a component in the PCB also allows you to wire something to that point if you need to test it or to modify the operation of the circuit - if you just leave it as no-connect there will not be a pad to wire to. In general, it is good practice to use a resistor if you ever need to pull a signal up to Vcc or down to ground, it provides flexibility in testing (for example you could disable the oscillator to inject another signal for testing) or easily modify the circuit.

This is internet...and you can read? I would try google or any other engine. Sometimes also a book can help. This is a collection of paper bound together.

It’s 32.768kHz, which is exactly dividable by 2^15 to give a 1 second period. Why not 16.384kHz? Probably size. The frequency is determined by the mass of the crystal, so a 16kHz crystal would be physically larger than a 32kHz and probably would not have fitted into the space available in digital watches of the 1980s. Since then it’s become a sort of industry standard, with 32.768kHz crystals being so cheap and plentiful that there is no point in changing it.