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I want to program an ATmega over JTAG, but I would like to build the JTAG programmer myself. Is it possible to program an ATmega128A by constructing a JTAG programmer similar to this?

It uses an FT232R FTDI chip from one of these boards:

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Connected to a JTAG header like this:

enter image description here

If this is possible, what software would I use to program with?

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This seems to be a generic FT232 breakout board. LadyAda has documented a way for using one to program an AVR chip (using avrdude). But it is really slow, and requires patching the avrdude software. So it is useful for writing a boot loader to the AVR, which you then can use for uploading your programs.

There is another guide which also provides some precompiled software based on avrdude (but as usual, beware with such software, and use a virtual machine to be sure).

But this only provides a way for programming the AVR. You don't get debugging capability that way. OpenOCD provides preliminary support for the 8-bit AVR family, so you might want to try this. The OpenOCD configuration is already provided with the programmer you linked to.

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  • \$\begingroup\$ it's ok, if it will be slow or doesn't have debugging capability, i just want to write flash memory \$\endgroup\$ – Alvin Jul 18 '12 at 14:15
  • \$\begingroup\$ Then avrdude-serjtag should work for you. \$\endgroup\$ – hli Jul 18 '12 at 14:34

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