LDCE - 2024.1 English

Primitive: Transparent Data Latch with Asynchronous Clear and Gate Enable

Introduction

This design element is a transparent data latch with asynchronous clear and gate enable. When the asynchronous clear input (CLR) is High, it overrides the other inputs and resets the data (Q) output Low. Q reflects the data (D) input while the gate (G) input and gate enable (GE) are High and CLR is Low. If (GE) is Low, data on (D) cannot be latched. 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) remains low.

This latch is asynchronously cleared, outputs Low, when power is applied. Power-on conditions are simulated when global set/reset (GSR) is active.

Logic Table

Inputs				Outputs
CLR	GE	G	D	Q
1	X	X	X	0
0	0	X	X	No Change
0	1	1	D	D
0	1	0	X	No Change
0	1	↓	D	D

Design Entry Method

Instantiation	Yes
Inference	Recommended
IP Catalog	No
Macro support	No

Available Attributes

Attribute	Type	Allowed Values	Default	Description
INIT	BINARY	0, 1	0	Sets the initial value of Q output after configuration.

VHDL Instantiation Template

Unless they already exist, copy the following two statements and paste them before the entity declaration.

Library UNISIM;
use UNISIM.vcomponents.all;


-- LDCE: Transparent latch with Asynchronous Reset and
--        Gate Enable.
--        7 Series
-- Xilinx HDL Language Template, version 2024.1

LDCE_inst : LDCE
generic map (
   INIT => '0') -- Initial value of latch ('0' or '1')
port map (
   Q => Q,      -- Data output
   CLR => CLR,  -- Asynchronous clear/reset input
   D => D,      -- Data input
   G => G,      -- Gate input
   GE => GE     -- Gate enable input
);

-- End of LDCE_inst instantiation

Verilog Instantiation Template


// LDCE:  Transparent latch with Asynchronous Reset and Gate Enable.
//        7 Series
// Xilinx HDL Language Template, version 2024.1

LDCE #(
   .INIT(1'b0) // Initial value of latch (1'b0 or 1'b1)
) LDCE_inst (
   .Q(Q),      // Data output
   .CLR(CLR),  // Asynchronous clear/reset input
   .D(D),      // Data input
   .G(G),      // Gate input
   .GE(GE)     // Gate enable input
);

// End of LDCE_inst instantiation

Related Information

7 Series FPGAs Configurable Logic Block User Guide (UG474)