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Electronics => Projects, Designs, and Technical Stuff => Topic started by: steaky1212 on July 13, 2013, 11:52:05 pm

Title: Datasheet clarification (specifically tie LOW on unused pins).
Post by: steaky1212 on July 13, 2013, 11:52:05 pm

Hi,

I'm using an OLED display with the SSD1306 controller.
I've been reading through the datasheet -> http://www.adafruit.com/datasheets/SSD1306.pdf (http://www.adafruit.com/datasheets/SSD1306.pdf) and pg15 instructs you to tie certain data pins low if using SPI.
Does this mean they should be connected directly to ground, or through a resistor?

Thanks,

Title: Re: Datasheet clarification (specifically tie LOW on unused pins).
Post by: Rerouter on July 13, 2013, 11:54:45 pm

i would recommend a pull-down resistance, while unlikely some displays have a pin that can function as an output for status, and you would not want that going to a short to ground

Title: Re: Datasheet clarification (specifically tie LOW on unused pins).
Post by: Mike Warren on July 16, 2013, 02:28:08 am

If it's a one-off, use resistor to be safe, but generally, "tie low" means connect to ground. A datasheet should explicitly state if a resistor is required.

Title: Re: Datasheet clarification (specifically tie LOW on unused pins).
Post by: amyk on July 16, 2013, 08:54:13 am

In SPI modes those are not used at all and the recommendation to tie low is to prevent them from floating. Directly to ground is fine.

Title: Re: Datasheet clarification (specifically tie LOW on unused pins).
Post by: KJDS on July 16, 2013, 09:25:00 am

If you're laying out a prototype board, then put in a standard sized 0R resistor and short it with a thin trace. That way you don't need to fit a resistor but can cut the track if you need to. If there may be a requirement in the future to pull it high, track in a resistor to Vcc too, it needn't be fitted until it's needed.