ILDXI

Transparent Input Data Latch (Asynchronous Preset)

ILDXI 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.

ILDXIs and IFDXIs

The ILDXI is actually the input flip-flop master latch. Two different outputs can be accessed 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 (ILDXI) corresponds to a falling edge-triggered flip-flop (IFDXI_1). Similarly, a transparent Low latch (ILDXI_1) corresponds to a rising edge-triggered flip-flop (IFDXI). Refer to the following figure for legal IFDXI, IFDXI_1, ILDXI, and ILDXI_1 combinations.

Figure 6.40 Legal Combinations of IFDXI and ILDXI for a Single IOB

Inputs			Outputs
GE	G	D	Q
0	X	X	No Chg
1	0	X	No Chg
1	1	1	1
1	1	0	0
1		D	d
d = state of referenced input one setup time prior to High-to-Low gate transition

Figure 6.41 ILDXI Implementation XC4000, Spartans

Figure 6.42 ILDXI Implementation Virtex