Re: open collector
In the fallowing ckt, what is your output with out the external resister conncted. Zer/floating. This type of output is Open Collector-Nothing conncted to collector of output transister. You can't drive anything with open collector outputs
If you use a pull up, the output changes between Vcc and Ground.
So you can connect any value of Vcc say 5v/24V. To give you an option to select the output level, it was left unconnected to a fixed value during manufacturing stage