Maximum trace length for JTAG lines

[gauravverma]

Hello,

In our T1024 based custom design, there are two T1024 processor..... we are able to connect with one T1024 through JTAG but not with other.....

We have checked all JTAG lines, power supply etc for other processor but with no outcome....

One difference i found between layout of two processors is length of JTAG lines.... For working processor trace length is between 4504 mills to 5553 mills and for not working processor it is between 7045 mills to 7818 mills ....

Does trace length impact its operation even though i am operating at very low speed aprox 100-500 KHz ??

Is there any limitation with respect to the  maximum trance length for JTAG lines ?

Regards

Gaurav

[yipingwang]

I do not think this is the cause of the problem. Please make sure that the two T1040 chips have identical schematics from JTAG/reset/supply/POR pin settings, etc. Also make sure that the two jatag connectors have same pinout, i.e, there is no mistake of layout to pin rows or columns or order, etc.  You might need to do so probing to the connector that does not work, search for opens, shorts, etc.

If this problem happen on all boards then there must be some real issue in the schematics/ manufacturing of the board.