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Observer dlrmsqja1
Registered: ‎05-29-2017


Hi guys! I'm using JTAG Cable xilinx platform cable Model DLC9G.


I have to control 4 CPLD by 1 JTAG port. Now I can put same code into 4 CPLD all at once. But I have to put 4 different code into 4 different CPLD each. I think that means I need 4 different TDI/ TDO port. Is it right? JTAG which now I'am using has just 1 TDO, 1TDI port, 1TCK port, 1TMS port. Do I have to use different JTAG CABLE? 

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2 Replies
Registered: ‎03-31-2016

Re: Multi JTAG TDI, TDO.

There is no such thing as a JTAG cable with multiple TDI and TDO ports.  JTAG is usually setup as a daisy chain, with TDO of one device connected to the TDI of the next but TMS and TCK go to all devices directly. iMPACT should show this representation.


Normally you cannot program more than one device at the exact same time, you should have to select each device individually, program it then wait for the completion to program the next one.  It does not matter if you select the same programming file for each or not.


If you have some custom board with a bad setup where only one device shows up iMPACT but all 4 get the same JTAG signals with TDO from one coming back to the header then you will have to look at the board design to figure out how to connect only one device to at a time to the JTAG header.

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Scholar drjohnsmith
Registered: ‎07-09-2009

Re: Multi JTAG TDI, TDO.

There are multi JTAG port pods, 

 but as stated above, you generaly don't use them.


This might be of use.





JTAG is a serial system, connect TDO out of one device to TDI of the next,

    The first device has its TDI to the programmer, the last device has its TDO connected to the programmer

              The TMS and TCK of all devices connect together, and to the programmer.



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