Answers Database

BOUNDARY SCAN/JTAG: Are there pullups/pulldowns in the TAP pins(XC4000, XC4000e, XC5200, XC4000EX)


Record #1577

Problem Title:
BOUNDARY SCAN/JTAG: Are there pullups/pulldowns in the TAP pins(XC4000,
XC4000e, XC5200, XC4000EX)



Problem Description:
Keywords: tap, bscan, jtag, boundary scan, tdi, tms, tck, tdo, pullup, pulldown

Urgency:standard

General Description:
If the TAP pins(TDI, TMS, TCK, and TDO) are not used as inputs/output to/from th
e
TAP, they can be used as I/O.  The TDI, TMS, and TCK pins can be used as
inputs, outputs,
tristated outputs,  and bidirectional pins.  The TDO can be used as an output on
ly,
or a tristated output.

Are there pullups/pulldowns available on the TAP pins?


Solution 1:

Pulldowns/pullups are available in the TDI, TMS, and TCK pins for non-boundary
scan operation.

TDO is a special case.	See Xilinx Solution 1358. See Xilinx Solution 1359



Solution 2:

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

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



End of Record #1577