Universal Scan Boundary Scan Test Software
    Boundary Scan Tools for the Rest of Us!
   

Test any JTAG device, any package, any vendor, anytime!


 

Application Note 004: JTAG Design considerations

What do you need to scan your own designs with Universal Scan? Just follow the guidelines below and you should be all set!

1. Obtain a BSDL file for each of the devices in your chain. Most manufacturers have these readily
    available on their web sites. (If possible, try to find a design with only one device in the chain - it 
    will make everything easier for your first attempt).

2. Make sure your scan chain is set up as follows:

JTAG scan chain diagram showing layout of TDI, TDO, TCK, TMS and TCK signals.

3. For best results, make sure the JTAG signals (TDI, TDO, TCK, TMS) are buffered as they enter/leave
    the board.

4. If you have more than a few devices in the chain, consider adding more buffers inline with the JTAG
    signals every few devices.  Try to group similar technologies together in the chain between buffers.

5. Make sure the power to the pod is appropriate for the pod you are using.

6. It is a good idea to make sure the JTAG Signals are accessible between the devices in the chain: if
    you have a major failure in one of the devices, you’ll be able to jumper around it and get the rest of
    the chain up and running.

7. Make sure the JTAG signals are pulled up and not left floating. (TRST is an optional signal that should
    be pulled low when not scanning).
 

Note: BSDL Files are notorious for having errors.  If you get an error message saying that something is wrong with your BSDL file, e-mail us a copy at techsupport@UniversalScan.com and we’ll attempt to get it fixed up for you.

Check out the parts manufacturers Web Sites for more information on designing with Boundary Scan.  They have a ton of information on how to design Scan into your system.

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