How to identify 3 states by 1 pin?

[adscrz]

How to identify 3 states by 1 pin?

In some remote control IC, like PT2262, 2272, there are 3 states:
VCC, GND, high resistance at address pin, what is the circuit
used in the IC internal ?

Thx

 

[arsenal]

for example,
you can do like this:
low
high
and the 3rd one: use some r,c to generate an oscillation

 

[chinara]

I believe this is a analog method in these chips.

 

[adscrz]

Someone advises:

% Add a "weak driver" to this input pin.
If it is floating, then the weak drive will dominate its state.
PS. you need to drive both high and low. (2 cycles)

Added after 29 minutes:

The figure is:

 

[nand_gates]

Here is one !dea how you can sense tri-state in a logic probe!
From the truth table you can distingush 'Z' from '0'

Hope this helps!

 

[Fom]

I didn't understand last circuit. If input is in high impedance state the base current of bipolar transistor will discharge input down to 0V. Why B should be 1?

 

[rambus_ddr]

Haha
PT2262 PT2272 PTI products!
The third state use two resitor create a VDD/2 voltage and use two VTH invert to creat 3 state code 11 01 10.

 

[aryajur]

I didn't understand last circuit. If input is in high impedance state the base current of bipolar transistor will discharge input down to 0V. Why B should be 1?

TTL Logic interprets High impedance as a 1, which can be understood by looking at the TTL logic. So B will be 1 at high impedance.