IOBUFDS - IOBUFDS - 2026.1 English - Primitive: Differential Input/Output Buffer

Primitive: Differential Input/Output Buffer

PRIMITIVE_GROUP: I/O
PRIMITIVE_SUBGROUP: BIDIR_BUFFER

Introduction

The IOBUFDS is a differential input/output buffer primitive. A logic-High on the T pin disables the output buffer. When the output buffer is 3-stated (T = High), the input buffer and any on-die receiver termination (uncalibrated or DCI) are ON. When the output buffer is not 3-stated (T = Low), any on-die receiver termination (uncalibrated or DCI) is disabled.

I/O attributes that do not impact the logic function of the component, such as IOSTANDARD, DRIVE, and SLEW, should be supplied to the top-level port via an appropriate property.

Logic Table

Inputs		Bidirectional		Outputs
I	T	IO	IOB	O
X	1	Z	Z	No Change
0	0	0	1	0
I	0	1	0	1

Port Descriptions

Port	Direction	Width	Function
I	Input	1	Input of OBUF. Connect to the logic driving the output port.
IO	Inout	1	Bidirectional diff_p port to be connected directly to top-level inout port.
IOB	Inout	1	Bidirectional diff_n port to be connected directly to top-level inout port.
O	Output	1	Output path of the buffer.
T	Input	1	3-state enable input signifying whether the buffer acts as an input or output.

Design Entry Method

Instantiation	Yes
Inference	No
IP and IP Integrator Catalog	No

Available Attributes

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;


-- IOBUFDS: Differential Bi-directional Buffer
--          7 Series
-- Xilinx HDL Language Template, version 2026.1

IOBUFDS_inst : IOBUFDS
generic map (
   DIFF_TERM => FALSE, -- Differential Termination (TRUE/FALSE)
   IBUF_LOW_PWR => TRUE, -- Low Power = TRUE, High Performance = FALSE
   IOSTANDARD => "BLVDS_25", -- Specify the I/O standard
   SLEW => "SLOW")       -- Specify the output slew rate
port map (
   O => O,     -- Buffer output
   IO => IO,   -- Diff_p inout (connect directly to top-level port)
   IOB => IOB, -- Diff_n inout (connect directly to top-level port)
   I => I,     -- Buffer input
   T => T      -- 3-state enable input, high=input, low=output
);

-- End of IOBUFDS_inst instantiation

Verilog Instantiation Template


// IOBUFDS: Differential Bi-directional Buffer
//          7 Series
// Xilinx HDL Language Template, version 2026.1

IOBUFDS #(
   .DIFF_TERM("FALSE"),     // Differential Termination ("TRUE"/"FALSE")
   .IBUF_LOW_PWR("TRUE"),   // Low Power - "TRUE", High Performance = "FALSE"
   .IOSTANDARD("BLVDS_25"), // Specify the I/O standard
   .SLEW("SLOW")            // Specify the output slew rate
) IOBUFDS_inst (
   .O(O),     // Buffer output
   .IO(IO),   // Diff_p inout (connect directly to top-level port)
   .IOB(IOB), // Diff_n inout (connect directly to top-level port)
   .I(I),     // Buffer input
   .T(T)      // 3-state enable input, high=input, low=output
);

// End of IOBUFDS_inst instantiation

Related Information

7 Series FPGAs SelectIO Resources User Guide (UG471)

IOBUFDS - IOBUFDS - 2026.1 English - Primitive: Differential Input/Output Buffer - UG953

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