# AVR Reset pin for a long time

I just have a little Question, if I drive a reset pin to low (reset active) of an Atmel AVR for a long time (1 week for example, in fact it'll be really variable depending on the use) can it cause default to the controller within a year or two ?

• You mean if it will damage the mcu in any way? The answer is no, it is not a problem. Dec 27 '13 at 14:26
• 1. Do you mean an Atmel AVR microcontroller? 2. What do you mean by "default to the controller"? Are you asking whether keeping the reset pin low will cause physical damage to the controller? (I don't know for sure, but I doubt it.) Dec 27 '13 at 14:27
• Yep, I had edited the post for other people to be sure ;) Dec 27 '13 at 14:29
• What is the power consumption like when its in this reset state? Feb 27 '15 at 3:19

No, this should not cause a problem. The one thing you need to worry about is the electrical state of the I/O pins during reset. Determine what state all of the I/O pins go to during reset (probably to input mode, perhaps with a weak pullup) and make sure that whatever is connected to them will not be damaged or cause damage to the AVR itself. Remember that all input pins should be held at a valid logic level and not allowed to float. This may mean that you need to add pullup or pulldown resistors in places where you might not otherwise need them.

EDIT: Additional information from the Atmel ATmega168 datasheet (I added emphasis for references to reset):

If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current consumption in all other modes where the digital inputs are enabled (Reset, Active mode and Idle mode).

The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or pull-down. Connecting unused pins directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is accidentally configured as an output

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• According to the AVR datasheet (for example mega88) The Port pins are tri-stated when a reset condition becomes active Dec 27 '13 at 14:35
• So I should set pull-ups, that's really not a problem Dec 27 '13 at 14:37
• Yes, if the ports are placed in a high impedance state it would be best to add pullup or pulldown resistors. These can be pretty weak (high resistor values). Dec 27 '13 at 14:42

While being in a reset state for a long time is not a problem, most AVR microcontrollers are programmed during reset. You'll therefore want to be very careful not to toggle the programming pins (in particular, the ICSP clock) while the chip is held in reset.

• Ι think it's unlikely to enter the programming mode by mistake because several bytes have to be send correctly in a sequence. Jan 5 '14 at 14:45
• Yes, but that's the same "unlikely" that motivated the fuse re-checking in avrdude. Given enough time it will happen. Jan 5 '14 at 16:53