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FD

D Flip-Flop

XC3000
XC4000E
XC4000X
XC5200
XC9000
Spartan
SpartanXL
Virtex
Macro
Macro
Macro
Macro
Macro
Macro
Macro
Primitive

figures/x3715n.gif

FD is a single D-type flip-flop with data input (D) and data output (Q). The data on the D inputs 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. For CPLDs, the power-on condition can be simulated by applying a High-level pulse on the PRLD global net. FPGAs simulate power-on when global reset (GR) or global set/reset (GSR) is active. GR for XC3000 is active-Low. GR for XC5200 and GSR (XC4000, Spartans, Virtex) default to active-High but can be inverted by adding an inverter in front of the GR/GSR input of the STARTUP or STARTUP_VIRTEX symbol.

Refer to the “FD4, 8, 16” section for information on multiple D flip-flops for the XC9000.

Inputs
Outputs
D
C
Q
0

0
1

1

Figure 5.4 FD Implementation XC3000, XC4000, XC5200, Spartans

Figure 5.5 FD Implementation XC9000

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