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Connecticut
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Many common MCUs (ATtiny's ATmega's etc) have a reset pin for programming them. The datasheets always talk about the "minimum pulse length." What is this, and how can you use the reset pin as a reset pin AND as a GPIO w/out triggering a reset?

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baum
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In short, you can't.

From the datasheet: "If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical char- acteristics of PC6 differ from those of the other pins of Port C.

If the RSTDISBL Fuse is unprogrammed, PC6 is used as a Reset input. A low level on this pin for longer than the minimum pulse length will generate a Reset, even if the clock is not running. The minimum pulse length is given in Table 28-12 on page 323. Shorter pulses are not guaran- teed to generate a Reset."

The RSTDISBL (reset disable) fuse determines if the pin is a Reset or I/O.
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So in my projects, I'm better off not using PC6 and just using the other 5?
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Just tuned in to this thread. Thanks James. That was very clear. I'm taking notes.  smiley
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So in my projects, I'm better off not using PC6 and just using the other 5?

Well, "better off" if you want the ability to RESET the processor.  If not, then it doesn't matter.
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So then what is RESET?
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I capitalized the word for emphasis.  I assume from your first post you are familiar with the concept of resetting a microcontroller.
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Reset is like the reset button on arduino (which is wired directly to reset pin). But why do I need to use reset w/ Arduino ISP? (which I will be using).

Thanks!
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The ISP programs the microcontroller's on-board flash ROM.  To make sure the processor is doing nothing while this occurs, the processor must be held in Reset.
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But why do I need to use reset w/ Arduino ISP? (which I will be using).
You cannot program the chip using the ISP (ICSP in Arduinospeak) pins  without the reset function enabled.  If you want to use the reset pin for I/O then you have to program the chip via a bootloader.

Don
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If you want to use the reset pin for I/O then you have to program the chip via a bootloader.
Or use high-voltage programming, although I admit that's something most Arduinoites would not be into.

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Rob
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But why do I need to use reset w/ Arduino ISP? (which I will be using).
You cannot program the chip using the ISP (ICSP in Arduinospeak) pins  without the reset function enabled.  If you want to use the reset pin for I/O then you have to program the chip via a bootloader.

Don

 Even with the bootloader, without a reset function the arduino auto-reset-before-uploading function will not work, so you will be trying to plug it into the USB (to get the power-up reset to bootloader) at just the right time to catch the upload handshake. I don't think that would work often enough before one gives up in disgust.

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