Answers Database

BOUNDARY SCAN/JTAG: Do Update Latches and Data Registers get reset in Test Logic Reset State?


Record #2195

Product Family:  Hardware

Product Line:  4000

Problem Title:
BOUNDARY SCAN/JTAG:  Do Update Latches and Data Registers get reset in
Test Logic Reset State?



Problem Description:
Keywords:  Test-Logic-Reset, Boundary Scan, JTAG, Update Latch
xc4000, xc5200

Urgency:  Standard

General Description:

What happens to the Update Latches and Data/Instruction Registers
of the boundary scan circuitry when the device enters the
Test-Logic-Reset state?  Do they get set or reset?


Solution 1:

When the device enters the Test-Logic-Reset state, the BYPASS
instruction becomes the current instruction and hence the
Instruction register and the Update latches are SET (output
HIGH).

The 1-bit BYPASS register is selected by the BYPASS Instruction.
The user may shift out the data in this register by performin
the shift-DR instruction.



End of Record #2195