Xilinx CPLD Libraries Guide

CR16CE
About Design Elements
Macro: 16-Bit Negative-Edge Binary Ripple Counter with Clock Enable and Asynchronous Clear
Supported Architectures
This design element is supported in the following architectures only:
• XC9500XL
• CoolRunner XPLA3
• CoolRunner-II
Introduction
This design element is a 16-bit cascadable, clearable, binary ripple counter with clock enable and asynchronous
clear.
Larger counters can be created by connecting the last Q output of the first stage to the clock input of the next
stage. CLR and CE inputs are connected in parallel. The clock period is not affected by the overall length of a
ripple counter. The overall clock-to-output propagation is n(tC - Q), where n is the number of stages and the time
tC - Q is the C-to-Qz propagation delay of each stage.
This counter is asynchronously cleared, outputs Low, when power is applied. .
Logic Table
Inputs Outputs
CLR CE C Qz – Q0
1 X X 0
0 0 X No Change
0 1 Ø Inc
z = bit width - 1
Design Entry Method
This design element is only for use in schematics.
For More Information
• See the appropriate CPLD User Guide.
• See the appropriate CPLD Data Sheets.
CPLD Libraries Guide
296 www.xilinx.com ISE 10.1