BCD to decimal decoders are common, but the ones I have looked at all have logic high/low states. Is there such a decoder that instead has a high-impedance (i.e., open) state and low state?

John

 

The high-impedance state is intended to isolate the logic element from the system. What would be the point?

 

Open collector?

 

Bill,
Open collector will work, I think. Is there a family that is open collector?

Beenthere,

At an abstract level, one can have: yes, no, and don't know/doesn't matter.

At a concrete level, I am playing with a set of resistors to make a digitally selectable output for a voltage regulator. The schematic has been shown on this forum. This is from the ST L200 datasheet:

That works easily with, say, 4 discrete values. I want to select voltages between 22 V and 12 V in 0.1 V steps. An ovbious way to do that is with BCD thumbwheel switch and BCD to decimal decoder on the board. By using either transistors or blocking diodes, I think I can get it done, but an open collector type of logic chip would make it easier.

John

 

After morning coffee, I was inspired to do more searching. It appears the SN74145, 54145, and 74LS145 are open collector.

Any others?

John