Reset button on Arduino UNO

Hi,

I am so sorry for asking a silly question but when the reset button on the arduino UNO is pressed what type of reset occurs. Is it a power on reset or an external reset? Thanks!

arduino-pgm-1912:
Hi,

I am so sorry for asking a silly question but when the reset button on the arduino UNO is pressed what type of reset occurs. Is it a power on reset or an external reset? Thanks!

Power On Reset and pulling the Reset Pin low are very similar. Although, each has its own Interrupt Flag.

Hi,

Thanks for your reply! Does that mean the arduino UNO implements a power on reset for the reset button on the board? I am asking since for my MCU the high fuse byte reads 0xDE which means the external reset is disabled.

High fuse byte 0xDE does not mean external reset disabled. The RSTDISBL fuse, if it were set, would turn the reset pin and button into a regular data pin instead of a reset pin. When you set that fuse, you would no longer be able to program it, unless you had a bootloader on the chip that works with a sufficient delay upon power up and you timed your programming right. Recovering normal operation would then require wiring up a high voltage programmer circuit.

Have a look at a fuse calculator: AVR Fuse Calculator for ATmega328P

And I forgot to mention, setting a fuse bit means it is 0 and unset is a 1. This is mentioned in the online fuse calculators and in the data sheet as "programmed" or "unprogrammed." It's the reverse of what most people would expect. So, high fuse byte of 0x5E would disable external reset, and therefore turn the reset pin into a regular data pin and require high voltage programming to recover.

Hi,

Pardon me but I do not understand whether 0 enables some function or disables the same function. For instance what does setting RSTDISBL to 1 do? Does it cause the PORT C pin to behave as active low reset pin?
Thanks!

arduino-pgm-1912:
Hi,

Pardon me but I do not understand whether 0 enables some function or disables the same function. For instance what does setting RSTDISBL to 1 do? Does it cause the PORT C pin to behave as active low reset pin?
Thanks!

Pardon me but did you GOOGLE RSTDISBL ?
I see 18,000 explanations, tutorials, examples and videos.
Did you view any of them?

If RSTDISBL is set to 1 it is unprogrammed and reset is not disabled. The reset pin acts as a reset pin and programming via ISP works ok.

If RSTDISBL is set to 0 the fuse is programmed. The reset pin does not work for reset and ISP programming, including setting other fuse values will no longer work. It is at this point most people consider the chip bricked, and if the program already loaded does not do what they want it to do, they throw the chip in the trash and just buy another since they are inexpensive.

Don't throw them away. Send them to me if you don't want them. I can fix them.

Yeah, HV programming sounds scary but it's not really all that bad and not expensive. You can experiment with those forbidden fuses and still recover. This is how I do it: http://www.instructables.com/id/HV-Rescue-Simple/