can external reset circuit connected with ISP programmer?

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#1
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hi all,

i have a doubt about the reset part for my project. I'm using an ISP interface programmer to program my ATMEGA32L. So i connected the MOSI, RST, SCK, and MISO pin from the programmer to my application board. I have an external reset circuit which is a pull up resistor and a push button one side to GND on my application board.

The doubt is, my external reset circuit is connected to my IC reset pin, but i have another connection between the ISP RST pin and my IC reset pin too. So means there are two different voltage going in my ATMEGA32L reset pin. Will this situation has any affect to my target IC?

thank you.

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Your ISP programmer will work finely until you press the "reset" button.

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haker_fox wrote:
Your ISP programmer will work finely until you press the "reset" button.

so do u mean that, even though there are two different voltage parallel going in to the reset pin but it wont burn that pin?

Or do i need to put a jumper there to select when programming i connect the IC reset pin to programmer reset pin , when running application i connect the IC reset pin back to the external reset circuit. Is it necessary to add this jumper?

thank you.

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From the application note i read from ATMEL.it says that, the reset line has to be kept at active low in order to enter and stay in programming mode.

So if i connect an external reset circuit to the target reset pin too, will the reset pin still able to be active low when entering programming mode.

thank you.

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Quote:
So if i connect an external reset circuit to the target reset pin too, will the reset pin still able to be active low when entering programming mode.

Your external reset circuit must not be push-pull, it needs to be open-drain, eventually with pull-up-resistor.

/Martin.

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Quote:
Your external reset circuit must not be push-pull, it needs to be open-drain, eventually with pull-up-resistor.

sorry.i not really understand how is your circuit looks like.If push-pull must not be used.Then how am i gonna reset my target IC?and with a open-drain circuit with it.

thank you.

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If you place a pullup-resistor on reset-pin, reset usually is high, this means normal operation of the mcu.
Your reset-circuit can reset your avr by pulling the reset-pin low as well as the programmer, which will also apply a low-level on reset during programming-mode.
There is no conflict, reset is active as one of the reset-circuits pulls the reset-pin low.

If your reset-circuit is push-pull, there will be a conflict during programming, because your reset-circuits wants reset to be high, the programmer wants it to be low. In this case you need a current limiting resitor (1-10K) in series to the push-pull output to allow proper operation.

/Martin.

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So the author can use its circuit because pull up resistor doesn't prevent to work finely. Of course the button must be unpressed.