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

Coding Badly

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


3.3V.

Coding Badly

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.


Ooh.  Good point.  LED needs to light both ways around to ensure the clock is running.


Quote
@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.


Is a series resistor between the clock source and XTAL1 pin necessary?  A good idea?

dc42


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


I'm not familiar with that device, but if you connect one of the channels to the CKOUT pin, then it should give you a frequency readout for that channel if there is a clock signal there.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

dc42


Is a series resistor between the clock source and XTAL1 pin necessary?  A good idea?


As I've very little idea what sort of impedance the resonator will present, I would use one for safety, but only 100 ohms or so.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Aakash

Nick,

I tried using -B250:
Code: [Select]
avrdude -p m328p -c avrispmkii -P usb -B250 -F

avrdude: stk500v2_command(): command failed
avrdude: stk500v2_program_enable(): bad AVRISPmkII connection status: Unknown status 0x00
avrdude: initialization failed, rc=-1
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x000000
avrdude: Yikes!  Invalid device signature.
avrdude: Expected signature for ATMEGA328P is 1E 95 0F



And regarding the high fuse question, I'm pretty sure. All I did was read in the fuse bits from the fresh chip and change the low bit by hand in AVR Studio. Though, I always could be mistaken.


@dc42 - I don't think CKOUT is outputting anything (see attached screenshot)

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