difference b/w normal output and open drain output of the pic

[puneetnepsam]

hi,

in the data sheet of the pic24f , it is written that every pin can behave as a normal digital output or a open drain output.
open drain output can be selected with the ODCx register.

can any one please tell me what is the difference between the two?

thanks
Puneet Gupta

 

[dknguyen]

A normal digital output can be driven HI and LOW by the PIC- it's what you would normally think of a digital pin.

Normal digital pins have a pull-up transistor and a pull-down transistor. One transistor pulls the pin HI (by connecting the pin to +V), and the other pulls the pin LO (by connecting the pin to GND). An open-drain output has no pull up transistor and only has the pull-down transistor. This means that instead of being able to make the pin go HI or LO like a normal digital pin, the pin can only go LO or high impedance/floating. This means you need a pull-up resistor to make the pin HI.

The "drain" on the LO transistor is "open" (not connected to a pull-up transistor). Open collector means the exact opposite (the drain on a MOSFET is the equivelant of the collector on a BJT)- it can go HI, but goes high impedance instead of going LO and a pull-down resistor is needed.

https://en.wikipedia.org/wiki/Open_collector

 

[Pommie]

The "drain" on the LO transistor is "open" (not connected to a pull-up transistor). Open collector means the exact opposite (the drain on a MOSFET is the equivelant of the collector on a BJT)- it can go HI, but goes high impedance instead of going LO and a pull-down resistor is needed.
Open collector - Wikipedia, the free encyclopedia

Open collector is either low or high impedance and a pullup is required. See your link,
**broken link removed**

Mike.

 

[puneetnepsam]

thanks for the information....

so in the normal pin case :
in pull up transistor if Vcc is equal 3.3V and if i make the pin high...pin will have 3.3 V...

in the open drain case , i want pin should have 5.5 V making it high,
so i have to connect pull up resistor to the 5.5V??