Answers Database

XC9500: What is the default value of tri-states for CPLDs?


Record #3194

Product Family:  Software

Product Line:  FPGA Core

Problem Title:
XC9500: What is the default value of tri-states for CPLDs?


Problem Description:
Keywords: Tri-state, 3-state, BUFT, BUFE, XC9500

Urgency: Standard


Solution 1:

For CPLD Outputs, there are four different ways to drive the
control line for the output buffer.

The signal can be tied either high or low, be driven by a
Global OE signal or be driven from the Product Term OE.

The polarity of the buffer is based upon which component is
used, either an OBUFT or OBUFE.

OBUFT - tri-state buffer with active low output enable
OBUFE - tri-state buffer with active high output enable

If no tri-state buffer is used and a simple OBUF is used, then
the enable line will default to '0'.



End of Record #3194