Libraries GuideChapter 7: Design Elements (LD to NOR16)
LDP
Transparent Data Latch with Asynchronous Preset
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
|
LDP is a transparent data latch with asynchronous preset (PRE). When the PRE input is High, it overrides the other inputs and resets the data (Q) output High. Q reflects the data (D) input while gate (G) input is High and PRE is Low. 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 remains Low.
The latch is asynchronously preset, output High, when power is applied. FPGAs simulate power-on when global set/reset (GSR) is active. For Virtex and Spartan2, 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
|
|---|
PRE
| G
| D
| Q
|
|---|
1
| X
| X
| 1
|
0
| 1
| 0
| 0
|
0
| 1
| 1
| 1
|
0
| 0
| X
| No Chg
|
0
| 
| D
| d
|
d = state of input one setup time prior to High-to-Low gate transition
|
