1 JTAG debugger multiple targets?

[lain.cai]

From what I've read it appears to be possible to debug daisy chained MCUs on a single PCB via a single JTAG connector, but is it possible to debug/flash multiple MCUs residing on their own PCBs each with their own JTAG connector? Thanks.

 

[barry]

You can daisy chain JTAG devices. The debugger doesn't know (or care) if they're on different PCBs or not.

 

[FvM]

I understand that you refer to chaining multiple JTAG connectors by a special made cable. Although this is possible by JTAG standard and should be supported by the involved tools, it may require a reduction of JTAG clock frequency or possibly buffering the common signals TCK and TMS. There might be also an issue of different voltage standards used by the JTAG interfaces, demanding for level conversion.

Multi-vendor JTAG chains are mainly used for boundary scan in-circuit test. For debugging and device programming during development, most people seem to prefer separate JTAG adapters for each device.

 

[lain.cai]

You can daisy chain JTAG devices. The debugger doesn't know (or care) if they're on different PCBs or not.

The problem is that I wouldn't be able to chain the PCBs together since they each have just one JTAG connector. I suppose people get around this using special adapters and such?

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I understand that you refer to chaining multiple JTAG connectors by a special made cable. Although this is possible by JTAG standard and should be supported by the involved tools, it may require a reduction of JTAG clock frequency or possibly buffering the common signals TCK and TMS. There might be also an issue of different voltage standards used by the JTAG interfaces, demanding for level conversion.

Multi-vendor JTAG chains are mainly used for boundary scan in-circuit test. For debugging and device programming during development, most people seem to prefer separate JTAG adapters for each device.

Thanks for the reply. I think the "specially made cable" that you mentioned is something I'm looking for. Are these things commercially available?

 

[FvM]

I think the "specially made cable" that you mentioned is something I'm looking for. Are these things commercially available?

I didn't come across yet. In my view, it's easy enough to make. As alrady mentioned, your JTAG adapter might face problems to drive a large number of TCK and TMS inputs plus cable capacitance in parallel. The required JTAG chain setup may be also inconvenient.

 

[lain.cai]

I didn't come across yet. In my view, it's easy enough to make. As alrady mentioned, your JTAG adapter might face problems to drive a large number of TCK and TMS inputs plus cable capacitance in parallel. The required JTAG chain setup may be also inconvenient.

I see. Thanks for the input.