ATtiny85 port pins floating

Go To Last Post
8 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

In using the ATtiny85 in a battery powered application I am looking for
the best pin setting for unused pins.
I am only using PB.0 as an output the other pins including RESET are floating at this
stage.

What is the best power conservation pin settings for the unused pins.

I am not clear if they should be set as output or inputs. Also, should pullup/pulldowns be be used.
I do have PUD set.

I would appreciate any advice on the various configurations for the unused pins.

Thanks for the help.

I'll believe corporations
are people when Texas executes one.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Either use the pull ups or set the pins as outputs and make them low for safety.
Well unless you decide to accidenatlly short them out to VCC. :-)

If you are NEVER going to use them then keep them as inputs and connect them to ground WITHOUT using pull ups.

Edit NOT the reset line of course.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Floating inputs are the worst. If they are around half-Vcc, then the input transistors are both in a high current state. So, tie either to Vcc or ground, with pull-up resistor off.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

CMOS parts draws power on transition (as opposed to ttl that draws power on logic level) so you need to have some defined logic level on the pins. I say that input with pull downs would be the "safest" ie will not destroy your part if a pin gets shorted.

edit: listen to they guys above.

link

i am a NOOO00B!!

Don’t let that undermine what I just said.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

OK, thanks for those inputs. I will take care
of setting them up. Hopefully that will lower
some of the power consumtion.

Quote:
keep them as inputs and connect them to ground WITHOUT using pull ups.

John, are you saying that I don't have to actually have resistors, just connect to GND(?).

lincoln, if I use plldowns I am thinking it
can be at least 10K or greater.

I'll believe corporations
are people when Texas executes one.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

10 k is a reasonable number, you just want some logic level. You don't want to tie pins directly to a power rail in case a pin gets set to output and a different value.

link

i am a NOOO00B!!

Don’t let that undermine what I just said.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
John, are you saying that I don't have to actually have resistors, just connect to GND(?).
Yep, however beware of what lincoln is saying. If you will NEVER need those pins and you are making lots of boards there is no point using the resistors.

The simplest thing at this stage is to try them as inputs with internal pull up resistors, measure the current.

Then switch off the internal pull up resistors, connect the pins to ground and measure the current.
If there is no notable difference just go with the internal pull up resistors and leave the pins not connected.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

OK folks , thanks. I just spent a little time viewing the videos for Alf (correct name?) Also, the RTOS were interesting......
Time to call it a night, I think.

I'll believe corporations
are people when Texas executes one.