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AR# 1577

JTAG - Are there pull-ups/pull-downs in the TAP pins (XC4000, XC4000e, XC5200, XC4000EX)?


If the TAP pins (TDI, TMS, TCK, and TDO) are not used as inputs/outputs to/from the TAP, they can be used as I/O. The TDI, TMS, and TCK pins can be used as inputs, outputs, 3-stated outputs, and bidirectional pins. The TDO can be used as an output only, or a 3-stated output.

Are there pull-ups/pull-downs available on the TAP pins?


Pull-downs/pull-ups are available in the TDI, TMS, and TCK pins for non-Boundary Scan operation.

For Boundary Scan operation, a default internal pull-up is active on TCK, TMS, and TDI inputs. This is in conformance with the IEEE 1149.1 standard.

The pull-ups are active by default for a device in JTAG mode before configuration, as well as after configuration with BSCAN module instantiated.

NOTE: In Xactstep 5.2.1/6.0.1, the TAP pins (TDI, TMS, TCK, TDO) may be left floating after configuration.

AR# 1577
Date Created 08/21/2007
Last Updated 12/15/2012
Status Active
Type General Article