Libraries GuideChapter 7: Design Elements (LD to NOR16)
LDCP_1
Transparent Data Latch with Asynchronous Clear and Preset and Inverted Gate
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
|
LDCP_1 is a transparent data latch with data (D), asynchronous clear (CLR) and preset (PRE) inputs. When CLR is High, it overrides the other inputs and resets the data (Q) output Low. When PRE is High and CLR is Low, it presets the data (Q) output High. Q reflects the data (D) input while gate (G) input, CLR, and PRE are Low. The data on the D input during the Low-to-High gate transition is stored in the latch. The data on the Q output remains unchanged as long as G remains High.
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
|
|---|
CLR
| PRE
| G
| D
| Q
|
|---|
1
| X
| X
| X
| 0
|
0
| 1
| X
| X
| 1
|
0
| 0
| 0
| 1
| 1
|
0
| 0
| 0
| 0
| 0
|
0
| 0
| 1
| X
| No Chg
|
0
| 0
| 
| D
| d
|
d = state of input one setup time prior to Low-to-High gate transition
|
