I have two questions that I was hoping someone could clarify with a quick True/False. When using the ATtiny85/85/2313 the reset pin is connected to a 10k resistor which is connected to VCC.
When programming with an AVR 6 pin programmer does the reset pin on an ATtiny at that point need to be connected to the 10k resistor to VCC?
When using an Arduino Uno to program an ATtiny, the reset pin on the attiny is connected to D10. Does the reset pin additionally also need to be connected to a 10k resistor to VCC?
Or to summarize does the reset pin on an ATtiny84/85/2313 always need to be connected to a 10k resistor to VCC?
Ben1234:
I have two questions that I was hoping someone could clarify with a quick True/False. When using the ATtiny85/85/2313 the reset pin is connected to a 10k resistor which is connected to VCC.
When programming with an AVR 6 pin programmer does the reset pin on an ATtiny at that point need to be connected to the 10k resistor to VCC?
When using an Arduino Uno to program an ATtiny, the reset pin on the attiny is connected to D10. Does the reset pin additionally also need to be connected to a 10k resistor to VCC?
Or to summarize does the reset pin on an ATtiny84/85/2313 always need to be connected to a 10k resistor to VCC?
Thanks in advance for your help!
I believe the reset pin is pulled high internally in the chip, so no external reset pull-up is required. At least that is my understanding.
During programming the reset pin will be taken low to reset the ATTiny. This will happen whether the reset pin is pulled high thru the external resistor or not. So it doesn't "need" to be connected to it, no. In fact it has a weak internal pull-up resistor itself so the external one is an additional failsafe to ensure the pin doesn't accidentally go low during operation and cause your project to randomly restart.
I don't think I've ever put an external pull-up on an ATTiny85 reset pin but out of habit I always do on the bigger ones. Doesn't mean that's best practice, I'm just saying I've yet to encounter any issues as a consequence.
The reset line has an internal pull-up resistor, but if the environment is noisy it can be insufficient and reset can therefore occur sporadically. Refer to datasheet for value of pull-up resistor on specific devices. Connecting the RESET so that it is possible to enter both high-voltage programming and ordinary low level reset can be achieved by applying a pull-up resistor to the RESET line. This pull-up resistor makes sure that reset does not go low unintended. The pull-up resistor can in theory be of any size, but if the Atmel AVR should be programmed from e.g. STK500/AVRISP the pull-up should not be so strong that the programmer cannot activate RESET by draw the RESET line low. The recommended pull-up resistor is 4.7k ? or larger when using STK500 for programming. For debugWIRE to function properly, the pull-up must not be smaller than 10k ?
Personally I've never used a pull up on my programmer boards used with ArduinoISP. If your USB ports are that noisy you've got worse problems than reset pullups.