Open collector concept.

[tkvenki]

Hi,

Can anybody help me out with the Open collector/drain concept in micro-controllers..
I know that these can sink more current.
I know that they must be oulled up in-order to use thenm as bi-directional ports.

But i need to know the basics of this concept.
Please help me out.

Venki

 

[Nigel Goodwin]

Hi,

Can anybody help me out with the Open collector/drain concept in micro-controllers..
I know that these can sink more current.
I know that they must be oulled up in-order to use thenm as bi-directional ports.

But i need to know the basics of this concept.
Please help me out.

There's hardly anything to know about it?, it's just a pin connected ONLY to the collector of a transistor (or the drain of an FET), no other components.

They DON'T sink more current (unless the transistor is a higher spec than the normal ones).

They also DON'T need to be pulled up to act as a bidirectional port, ONLY if it needs to source current rather than sink it when set as an output.

There are basically two advantages to it, firstly it's useful for a common line (like I2C), where setting it HIGH means the line is free to be controlled elsewhere. Secondly, it allows you to switch higher voltage rails, as the pin can be pulled higher by a pullup resistor.

 

[tkvenki]

Thanks a lot for your reply Nigel