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AR# 8900

JTAGProgrammer - SVF Generation: what do the two options for the initial transition to Run-Test/Idle mean?


Keywords: SVF, XSVF, JTAG, JTAG Programmer, Run-Test/Idle, Test-Logic-Reset

Urgency: Standard

General Description:
When selecting to create an SVF via the JTAG Programmer, there are two options for the initial transition to Run-Test/Idle. These options are:

a) through Test-Logic-Reset
b) skipping Test-Logic-Reset

What do each of these options mean, and how does it affect the SVF


JTAG Programmer generates an initial "STATE" command in the SVF. The
SVF "STATE" command tells a JTAG controller to take the TAP state machine
to a particular state.

Option (a) generates:

Option (b) generates:

For option (a), the RESET in the "STATE" command suggests to the JTAG
controller that it should select a path through the TAP state machine that
passes through the Test-Logic-Reset state on its way to the Run-Test-Idle state.

Only when the user can, and wants to control the TAP state sequencing for
special purposes should you select the "skipping Test-Logic-Reset" option.

Typically, the option selection does not matter. Test-Logic-Reset incurs no
unusual effects in Xilinx devices. In most cases, the JTAG controllers force
the TAP controller through Test-Logic-Reset on startup to insure a known
starting state. Furthermore, most JTAG controllers ignore the intermediate
state paths within an SVF "STATE" command and proceed to the final state
on their own terms. In fact, the initial transition option has no affect among
the supported ATE nor XSVF (Xilinx XAPP058) solutions.
AR# 8900
Date 09/30/2005
Status Archive
Type ??????