CARRY4 - 2021.2 English

Vivado Design Suite 7 Series FPGA and Zynq-7000 SoC Libraries Guide (UG953)

Document ID
UG953
Release Date
2021-10-22
Version
2021.2 English

Primitive: Fast Carry Logic with Look Ahead

Introduction

This circuit design represents the fast carry logic for a slice. The carry chain consists of a series of four MUXes and four XORs that connect to the other logic (LUTs) in the slice via dedicated routes to form more complex functions. The fast carry logic is useful for building arithmetic functions like adders, counters, subtracters and add/subs, as well as such other logic functions as wide comparators, address decoders, and some logic gates (specifically, AND and OR).

Port Descriptions

Port Direction Width Function
O Output 4 Carry chain XOR general data out.
CO Output 4 Carry-out of each stage of the carry chain.
DI Input 4 Carry-MUX data input.
S Input 4 Carry-MUX select line.
CYINIT Input 1 Carry-in initialization input.
CI Input 1 Carry cascade input.

Design Entry Method

Instantiation Yes
Inference Recommended
IP Catalog No
Macro support No

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;

-- CARRY4: Fast Carry Logic Component
--         7 Series
-- Xilinx HDL Language Template, version 2021.2

CARRY4_inst : CARRY4
port map (
   CO => CO,         -- 4-bit carry out
   O => O,           -- 4-bit carry chain XOR data out
   CI => CI,         -- 1-bit carry cascade input
   CYINIT => CYINIT, -- 1-bit carry initialization
   DI => DI,         -- 4-bit carry-MUX data in
   S => S            -- 4-bit carry-MUX select input
);

-- End of CARRY4_inst instantiation

Verilog Instantiation Template


// CARRY4: Fast Carry Logic Component
//         7 Series
// Xilinx HDL Language Template, version 2021.2

CARRY4 CARRY4_inst (
   .CO(CO),         // 4-bit carry out
   .O(O),           // 4-bit carry chain XOR data out
   .CI(CI),         // 1-bit carry cascade input
   .CYINIT(CYINIT), // 1-bit carry initialization
   .DI(DI),         // 4-bit carry-MUX data in
   .S(S)            // 4-bit carry-MUX select input
);

// End of CARRY4_inst instantiation

Related Information

  • See the 7 Series FPGAs Configurable Logic Block User Guide (UG474).