Hi,
I have a little question about using the RESET pin as an i/o pin. I have read somewhere that it can be used as a “weak” i/o pin, not exactly knowing what weak means. So I just tried to flash an LED with it. It works, but REALLY “weakly”. I was just wondering if the reset pin is really that weak or if I can set something to make it brighter w/o using any additional external components.
Thank you!!
Robert
Hello.
Which microcontroller are you referring to? Are you using the microcontroller by itself or is it part of a controller board?
- Ben
Hi Ben,
sorry for the incomplete post. I am using an ATtiny45. I am just using the MCU, but no controller board. So there is basically just one button further LEDs on other pins and the power supply.
Thanks again
-Robert
It’s important you specify which MCU you’re using since different chips have different electrical properties. Initially I assumed you were talking about the ATmega168, which we feature in most of our Orangutan robot controllers, but I could find no mention of weak driving strength on the RESET line. However, the datasheet for the ATtiny45 does mention that the RESET line can only function as a weak I/O. Take a look at note 6 on page 167; this note points you to several figures that show the electrical characteristics of the RESET pin when it’s used as a general-purpose digital I/O.
Out of curiosity, can you still program the MCU as normal after you’ve changed the fuses to turn the RESET line into a digital I/O? I was never sure what would happen since the standard ISP programming process transmits SPI commands while RESET is held low.
- Ben
Hi Ben,
thanks for the hint. That explains the weak capability of driving an LED. I am using a MOSFET now to get the LED bright.
The AVR cannot be programmed via ISP when the reset pin is disabled. I know that using a bootloader works and I am pretty sure I have read that high voltage programming can be used, too. However, I cannot find where I read this. I’ll let you know when I find it.
-Robert
