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Libraries Guide
Chapter 7: Design Elements (LD to NOR16)

LDE

Transparent Data Latch with Gate 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

LDE is a transparent data latch with data (D) and gate enable (GE) inputs. Output Q reflects the data (D) while the gate (G) input and gate enable (GE) are High. The data on the D input during the High-to-Low gate transition is stored in the latch. The data on the Q output remains unchanged as long as G or GE remain Low.

The latch 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
GE
G
D
Q
0
X
X
No Chg
1
1
0
0
1
1
1
1
1
0
X
No Chg
1

D
d
d = state of input one setup time prior to High-to-Low gate transition