# Turn pull-up into pull-down

I have come across the following problem a few times in the past:

You have a break-out board where some pins have already been pulled up or down for convenience, e.g. RESET pulled high to keep the board running even when you don't connect the input pin to your MCU. Now you want the opposite standard behaviour when the pin is not set (e.g. in sleep mode or when no power is applied to the MCU). How can you achieve this? The only answer I can think of is to (physically) remove the pull-up and hook a pull-down between the MCU and the break-out board. I would rather not mess with the SMDs on the break-out board, so is there another solution?

A concrete example is an audio amplifier that is by default on and needs to be pulled down by a pin to switch off. Now when I remove power from the MCU, it automatically turns on again and pops audibly.

Yours gratefully Jerome

• Do you mean you want change the default working mode, change the default high to default low without remove the pull-up? – diverger Nov 6 '14 at 10:33
• A schematic would help us see the problem better. – Ricardo Nov 6 '14 at 10:36

• @MampomatWhat would be the advantage of this solution over a simple pull-down with lower resistor values? Lower power wasted than when pulling up a small resistor. Would your solution be more power-efficient? Depends on how long the small pulldown was pulled up. – EM Fields Nov 6 '14 at 12:28