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AR# 24167

CPLD Frequently Asked Questions for XC9500/XL/XV and CoolRunner-II/XPLA3 families


Below are some of the most Frequently Asked Questions by CPLD designers.


What are some good design practices to follow when using a Xilinx CPLD?

Refer to (Xilinx XAPP784): Bulletproof CPLD Design Practices

How do I program a Xilinx CPLD?

Refer to (Xilinx Answer 7585)

How are the initial states of registers set?

Refer to (Xilinx Answer 3123)

How do the global buffers work (GTS, GSR, GCK)?

Refer to (Xilinx Answer 3122)

What is the state of I/O during power up and power down?

Refer to (Xilinx Answer 7648)

How do I prevent the tools from using a particular I/O pin?

Refer to (Xilinx Answer 1987)

Are there best-case (minimum) timing numbers available?

Refer to (Xilinx Answer 17006)

What decoupling recommendations exist for Xilinx CPLDs?

Refer to (Xilinx Answer 7621)

Where can I see an I/V curve for the CPLD I/O?

Refer to (Xilinx Answer 3116)

How do I internally source global signals such as GCK or GTS?

Refer to (Xilinx Answer 5572)

How much current can I sink or source from an I/O pin ?

Refer to (Xilinx Answer 5770)

What should I do with my unused I/O pins?

Refer to (Xilinx Answer 8458)

What should I do with my unused JTAG pins?

Refer to (Xilinx Answer 1408)

How can I use the internal pull-up resistor in a 9500/XL/XV device?

Refer to (Xilinx Answer 3026)

How much power can I sink into a CPLD?

Refer to (Xilinx Answer 1308)

How do I create an open-drain output?

Refer to (Xilinx Answer 1651)

How do I control power consumption in a 9500/XL/XV device?

Refer to (Xilinx Answer 2717)

XPLA3 : How does the Port Enable pin work?

Refer to (Xilinx Answer 8455)

XPLA3 XC9500XL/XV : How do I drive 5V logic from a 3.3V/2.5V device?

Refer to (Xilinx Answer 6717)

Where can I find a CPLD Demo board?

Refer to (Xilinx Answer 7855)

Where can I find information on how to use the CoolRunner-II advanced features such as DataGate or CoolClock?

Refer to (Xilinx XAPP378): Using CoolRunner-II Advanced Features

Which CPLDs have 5V tolerant I/Os?

The XC9500, XC9500XL, and CoolRunner XPLA3 CPLDs have 5 Volt tolerant I/Os. 

For CoolRunner-II, an application note exists describing how to add circuitry to make it 5 Volt-tolerant. - (Xilinx XAPP429): 5V Tolerance Techniques

How do I estimate power consumption of my CPLD?

The CoolRunner XPLA3 and CoolRunner-II devices are supported in XPower. 

XPower requires a completed design to function. For the XC9500/XL/XV families, there is a power estimation equation on the front page of the respective family data sheet. 

CoolRunner-II has a similar method of power estimation described in (Xilinx XAPP317): Power Evaluation for CoolRunner-II.

Can I use a crystal or RC oscillator with my Xilinx CPLD?

This is not recommended with Xilinx CPLDs. The frequency generated by such an oscillator is typically too unstable since it can vary with voltage and temperature.
AR# 24167
Date 09/19/2017
Status Active
Type General Article
  • CoolRunner-II
  • CoolRunner XPLA3
  • 9500
  • More
  • 9500XL
  • 9500XL IQ
  • 9500XL XA
  • 9500XV
  • CoolRunner-II XA
  • Less
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