Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Eight questions concerning j-tag

Not open for further replies.


Advanced Member level 3
Oct 24, 2005
Reaction score
Trophy points
Sunnyvale, California, USA
Activity points
some questions on j-tag

I would like to understand the jtag. Maybe if I design a board with embedded jtag controller in the future?
So, I have some questions on that:

1.) How can a BS controller recognize the devices in a chain? Automatic recogition. Is it possible? Should I know the IDCODEs to recognize? Or BSDL? Are all idcodes 32bit?

2.) How can the BS controller select one IC from the many ICs in the chain, to give a commad to that? and only for that one. After that, what do the others? For what time or until what event?

3.) If a test is running in one IC, why do not recognizes the other ICs in the chain the datastream (some pattern) as commands?

4.) What is after system-reset? and after that? Who gets the first command?

5.) how can I accees to the n. device and after that, the n+1. ? or n-1. ?

6.) what is the difference between a command, and some data? how can I select, what is what the IC gets in the TDI? How can I say that: this is a command.

7.) Is there any standard, on command/bscan register lengths?

8.) Can all jtag devices operate in a chain? or some only in standalone tested device? The boundary scan controllers? Can all scan a chain with more than one jtag compliant device? I red through some SN74LVT8980-like datasheets, but it was not clear for me.

Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com