Hi to everyone:
I was showing an electronic design to one friend and he told me I should always use a "pull-down" resistor for permanently grounding a negated pin in a chip (previously I had it connected to GND - 0V).
Can someone explain the reason of that? or some source of information?
Best Regards...
Franco.
The idea is usually just that it's a lot easier to undo if you change your mind and need to use the pin for something after all. :-)
For engineering prototypes, it's one of those things where it "can't hurt, might help." For production boards, at least for high volumes, most people would choose to save the money by tying to ground as you've done.
Great and honest answer.
This pin is normally driven by a uC, so if I want to change the design I will connect the uC which has an internal pull-up resistor in this case.
I have a big problem with the space in this board (it is a 4 layer
25mm diameter circle!!!). So, even an 0603 SMD component is painful.Best Regards...
Franco.
You may also be able to program the pin as an output and leave it floating. If it cannot be programmed as an output, then there is little reason to use a resistor.
Some kind of RF or RFID gadget?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Mmmm, no. It is a little controller board for a robotic application.
Thanks for the answers...
Franco.
An automated test machine will want to drive any pin either high or low. It can't drive a pin that is connected to either gnd or vcc. 220 Ohms is a good value for a pulldown. Same goes for unused functions; you will want these to work.
Tam
Tam/WB2TT t-tammaru@c0mca$t.net posted to sci.electronics.design:
Not really. I do not know of any that were not "fully programmable" even 25+ years ago. They tested what they were told to. The expensive complex ones, even then, had a modest computer (high range pdp-11's running rsx-11) running the controls of the hardware and logging the test results. And "bed of nails" tester configurations were being abandoned in favor of early JTAG; the speeds were starting to really climb and pin driver electronics and fixturing was getting really difficult.
I agreee with you, but pin testing is where the rules concerning pullups and pulldowns came from.
Tam
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.