Multi Microcontroller programming with single JTAG port ...

[Oveis.Gharan]

Dear all,
Is it possible to program several AVR microcontroller in a board whit single JTAG port on a board. I want to know if i want to desig a board that has more than one microcontroller which thay have different codes, is it possible to have single JTAG port, or i must put JTAG ports for each microcontroller?

Thanks in advance.

 

[RetroTechie]

In principle JTAG ports can be 'daisy-chained' together to form a JTAG chain - basically TDO from 1st device goes to TDI from 2nd device, TDO from 2nd device goes to TDI from 3rd device etc, and the other signals are connected in parallel between devices. See here for an idea: Joint Test Action Group - Wikipedia

But I can imagine it depends on software that comes with a programmer, whether or not you can select individual devices in such a chain. Perhaps you could do a quick 'n dirty hookup of a few of these AVR microcontrollers, and check if programmer software sees them separately?

 

[Oveis.Gharan]

Dear Retro
I am so appretiated for your helpful comments.
Yes, I think the softwares which i use for programming seems not to have the option to chain microcontrollers. Could you give more information about the JTAG?
Is there any useful, and comprehensive manual about JTAG? I want to know how can i develop a system that all the devices could be tested with single JTAG port!

Best Regards.
Thanks in advance.
Please keep in touch.
Oveis

 

[FvM]

AVR processors have a known restriction, that their fast programming algorithm only works for the first device in a JTAG chain. Generic JTAG programming commands works however. I'm not sure about processor debugging support, basic boundary scan should work in a chain.