Current limiting resistors?

blackbox_dev · Post by **blackbox_dev** » Tue Sep 23, 2008 8:17 pm

Is it a good practice to put current limiting resistors on the paths between a microcontroller and the ICs that connect to it? I'm thinking that it might be needed if one device drives the line high and the other drives it low, because otherwise it would result in a short. However, I haven't seen it done in other circuits. What would be a good value to use if the resistors are used? 1K?

-dev

blackbox_dev · Post by **blackbox_dev** » Sun Sep 28, 2008 9:37 am

Can anybody help? There's been 55 views!
the sad thing is that if this was posted in F42 it would have taken less than a day to get answered...

superdeformed · Post by **superdeformed** » Sun Sep 28, 2008 10:06 am

I've never seen it done before either. The only time I can think of that you might run into the problem you described would be if you have a bi-directional device (or something isn't working right, in which case you have other problems). If that is the case you may be able to configure the I/O pins on the microcontroller as tri-state buffers, otherwise you can put in your own buffer (you can get them with several in a single IC package). Assuming the ICs you're connecting to are bi-directional, they probably have or need a read/write signal which you can use to control the direction of the buffer.

A resistor would probably work depending on how many devices you're trying to drive off the pin and what the internals of your ICs look like. The size would depend on how much current your devices can safely source or sink, and you'll also have to keep in mind the impedances of the inputs and the minimum current you need on each pin for it function properly.

blackbox_dev · Post by **blackbox_dev** » Sun Sep 28, 2008 12:02 pm

OK, thanks for the answer. Since the resistor is the simplest option I'll go with that. Now, it's back to the datasheets.

-dev