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Topic: [SOLVED] Set Low Fuse Bit, Now Can't Program over ISP (Read 6 times) previous topic - next topic

Nick Gammon

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...am having a slightly big issue ...


A small issue?

You have set the "divide by 8" fuse. If you slow down programming you can probably talk to it.

Nick Gammon

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Does the resonator have to be removed?


No.

Aakash

@Coding Badley - the system runs at 3.3V, when selecting the current limiting resistor should I account for that voltage or a lower one?

@dc42 - I have Saleae Logic analyzer, should I be able to use that to test if there is a signal being outputted?

@Nick - Should I go lower than -B5 rate?

Thanks for the help everyone!

Aakash

dc42


Connect an LED + current limiting resistor.  If the LED lights, the resonator is running.  If the resonator is running, you can reprogram the processor; it's just a matter of getting the ISP bitrate low enough.


Don't you need to connect the LED+resistor between the pin and ground, and then between the pin and Vcc, and check it lights in both cases? I wouldn't like to guess what state the CKOUT pin will have when there is no clock.


@dc42: Does the resonator have to be removed?  Will it be damaged by a clock signal on XTAL1?


I don't think there is any danger of damaging the resonator if you leave it in place. However, the resonator will present quite a low impedance at frequencies that are not very close to its resonant frequency, and the signal from XTAL2 will provide negative feedback via the resonator to XTAL1. So it may be difficult to provide enough drive from the clock source, unless you match the resonator frequency. I guess it's worth trying with the resonator connected first.
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Nick Gammon


@Nick - Should I go lower than -B5 rate?

-B5?

I set mine to run at 128 KHz and could reprogram it with -B250. So, no.

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@dc42 - I have Saleae Logic analyzer, should I be able to use that to test if there is a signal being outputted?


I don't think that's relevant.

Have you reprogrammed the high fuse by any chance?

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