UG445 Datasheet, PDF (9/24 Pages) –

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CPLD I/O User Guide
Terminations
Terminations are a vital aspect of a robust transmission line. The on-chip termination of the
CPLD I/Os eliminate the need for external termination. It is strongly recommended not to
float CMOS inputs as this increases power. The on-chip termination of the CPLDs can be
used to minimize power without the need for external components. The following section
discusses the termination options available in the different CPLD families and how to
utilize the features.
Termination Options
The user can select the termination type for the unused I/Os and the Input and Tristate
I/Os separately.
For the Input and Tristate I/O termination mode, the options are (default in parentheses):
Note: Bus-hold and Keeper terms can be used interchangeably.
• XC9500 XL/ XV: Float, Keeper (keeper)
• CoolRunner™ XPLA3: Float, Pull-up (pull-up)
• CoolRunner™-II: Float, Pull-up, Keeper (keeper)
For the unused I/Os, the options are (default in parentheses):
• XC9500 /XL/XV: Float, Ground (float)
• CoolRunner XPLA3: Float, Pull-up (pull-up)
• CoolRunner-II: Float, Ground, Pull-up, Keeper (ground)
For CoolRunner-II devices, it is possible to have a combination of multiple termination
modes for used and unused I/Os. However, not all combinations are possible. Table 1 lists
permitted combinations.
Table 1: Input Termination Schemes
Possible Input Termination Schemes
All Pull-up
All Bus-hold
Combination of Pull-up and Float
Combination of Bus-hold and Float
All Float
CPLD I/O User Guide
www.xilinx.com
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UG445 (v1.2) January 14, 2014