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ILDI

Transparent Input Data Latch (Asynchronous Preset)

XC3000
XC4000E
XC4000X
XC5200
XC9000
Spartan
SpartanXL
Virtex
N/A
Macro
Macro
N/A
N/A
Macro
Macro
Macro

figures/x4388n.gif

ILDI is a transparent data latch, which can hold transient data entering a chip. When the gate input (G) is High, data on the input (D) appears on the output (Q). Data on the D input during the High-to-Low G transition is stored in the latch.

The latch is asynchronously preset, output High, when power is applied. FPGAs simulate power-on when global set/reset (GSR) is active. GSR (XC4000, Spartans) default to active-High but can be inverted by adding an inverter in front of the GSR input of the STARTUP symbol.

ILDIs and IFDIs

The ILDI is actually the input flip-flop master latch. It is possible to access two different outputs from the input flip-flop: one that responds to the level of the clock signal and another that responds to an edge of the clock signal. When using both outputs from the same input flip-flop, a transparent High latch (ILDI) corresponds to a falling edge-triggered flip-flop (IFDI_1). Similarly, a transparent Low latch (ILDI_1) corresponds to a rising edge-triggered flip-flop (IFDI).

Refer to the following figure for legal IFDI, IFDI_1, ILDI, and ILDI_1 combinations.

Figure 6.30 Legal Combinations of IFDI and ILDI for a Single IOB in XC4000 and Spartans

Inputs
Outputs
G
D
Q
1
1
1
1
0
0
0
X
d
d = state of referenced input one setup time prior to High-to-Low gate transition

Figure 6.31 ILDI Implementation XC4000, Spartans

Figure 6.32 ILDI Implementation Virtex

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