Answers Database
JTAG - Are there pullups/pulldowns in the TAP pins(XC4000, XC4000e, XC5200, XC4000EX)
Record #1577
Problem Title:
JTAG - Are there pullups/pulldowns in the TAP pins(XC4000, XC4000e, XC5200, XC4000EX)
Problem Description:
Urgency:standard
General Description:
If the TAP pins(TDI, TMS, TCK, and TDO) are not used as inputs/output to/from the
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 only,
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.
Note: In Xactstep 5.2.1/6.0.1, the TAP pins (TDI, TMS, TCK,
TDO) may be left floating after configuration.
End of Record #1577 - Last Modified: 01/10/00 22:12 |
