Yes....I know.....basic......but I have to ask what this termology means in the form of changing a pin on a processor from an open drain to a push pull...thanks....
Open drain and push-pull
Dec 30, 2003
2 Replies
An open drain can only sink current. You use it for wired-OR bus connections. It requires an external pull-up resistor.
A push/pull can source or sink current. It MAY OR MAY NOT have a third high-impedance state in which it does neither.
A push/pull does not require an external pull-up resistor UNLESS it also supports the high-impedance state.
You generally will only use the tri-state ones for bus connections. You can tie many tri-state outputs together, sharing a pull-up, but you have to be careful to make certain that you don't have two of them trying to drive the bus in different directions at the same time.
Think of a SPDT switch. The arm is the output pin. Connect the lower terminal to ground, and leave the upper terminal open. You have an open drain output. Connect the upper terminal to the plus logic voltage. You have a push pull output.
+V (or open) ---------o 1 -----o-----------> output. GND ------------------o 0
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
USE worldnet address!
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required