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Libraries Guide
Chapter 5: Design Elements (F5MAP to FTSRLE)

FDE

D Flip-Flop with Clock Enable

XC3000
XC4000E
XC4000X
XC5200
XC9000
Spartan
SpartanXL
Spartan2
Virtex
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Primitive
Primitive

FDE is a single D-type flip-flop with data input (D), clock enable (CE), and data output (Q). When clock enable is High, the data on the D input is loaded into the flip-flop during the Low-to-High clock (C) transition.

The flip-flop is asynchronously cleared, output Low, when power is applied. Virtex and Spartan2 simulate power-on when global set/reset (GSR) is active. GSR defaults to active-High but can be inverted by adding an inverter in front of the GSR input of the STARTUP_SPARTAN2 or STARTUP_VIRTEX symbol.

Inputs
Outputs
CE
D
C
Q
0
X
X
No Chg
1
0

0
1
1

1