I'm a bit confused by things I've read, written by a variety of sources and cannot find conclusively whether or not a bootloader can be erased using my rig.
I have a bare bones programming board consisting of a 6 pin dip header for ISP connection to an AVRisp MKII and a 28 pin Ziff socket. Nothing more. The isp has been modified to power the m328p via USB power. Simple. I have some chips that have a bootloader on them. I'd like to erase the bootloader, but the initialization keeps failing. Avrdude says the signature of the chip doesn't match what's expected. I'm guessing that's because of the bootloader?
I saw somewhere, and can't find it now, something to the effect that one certain fuses are set a certain way, that the only way to get them back is by providing an external signal. That a crystal and a couple caps wouldn't do. If I do need an external clock signal, what's the easiest way to implement that on my basic programmer board? I would think I might even be able to tap into a signal on the avrisp, no?
Bottom line, I'm just looking for a way I can erase bootloaders using the same rig I use for ISP programming.
chipwitch:
I'm guessing that's because of the bootloader?
No.
I saw somewhere, and can't find it now, something to the effect that one certain fuses are set a certain way, that the only way to get them back is by providing an external signal. That a crystal and a couple caps wouldn't do.
Incorrect.
If I do need an external clock signal, what's the easiest way to implement that on my basic programmer board?
Add a crystal + capacitors or a resonator.
Bottom line, I'm just looking for a way I can erase bootloaders using the same rig I use for ISP programming.
See above.
An alternative to crystal + capacitors or a resonator is to provide a reasonable clock signal on the XTAL1 pin. There are ArduinoISP versions available that output such a clock signal.
I saw somewhere, and can't find it now, something to the effect that one certain fuses are set a certain way, that the only way to get them back is by providing an external signal. That a crystal and a couple caps wouldn't do.
It is possible to "brick" a chip like this, by configuring the fuses for "external oscillator" instead of "external crystal", but this is not something that would usually happen during bootloader programming (it IS a common mistake for new users trying to set the fuses based on the AVR datasheet.)
The bootloader is not involved at all when you are doing ISP programming, but the process of burning the bootloader for an Arduino also involves setting the fuses. This is normally done by the IDE's "burn bootloader" command, or the bootloader's Makefile, but it's possible to burn the bootloader via ISP manually, and either forget to change the fuses, or set them wrong.
Thanks, that link is what I was looking for. I'd seen it once before, read part of it and moved on. It was before I had ever used avrdude. I knew there was "something" I'd read about a crystal wouldn't do. The distinction between fuse settings of oscillator and crystal didn't sink in. Got it now. Thanks again to you both.