Primitive: Differential 3-state Output Buffer
- PRIMITIVE_GROUP: I/O
- PRIMITIVE_SUBGROUP: OUTPUT_BUFFER
Introduction
The OBUFTDS is a differential 3-state output buffer primitive.
I/O attributes that do not impact the logic function of the component, such as IOSTANDARD and SLEW, should be supplied to the top-level port via an appropriate property.
Logic Table
| Inputs | Outputs | ||
|---|---|---|---|
| I | T | O | OB |
| X | 1 | Z | Z |
| 0 | 0 | 0 | 1 |
| 1 | 0 | 1 | 0 |
Port Descriptions
| Port | Direction | Width | Function |
|---|---|---|---|
| I | Input | 1 | Buffer input. |
| O | Output | 1 | Diff_p output. Connect directly to a top-level port in the design. |
| OB | Output | 1 | Diff_n output. Connect directly to a top-level port in the design. |
| T | Input | 1 | 3-state enable input. |
Design Entry Method
| Instantiation | Yes |
| Inference | No |
| IP and IP Integrator Catalog | 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;
-- OBUFTDS: Differential 3-state Output Buffer
-- 7 Series
-- Xilinx HDL Language Template, version 2026.1
OBUFTDS_inst : OBUFTDS
generic map (
IOSTANDARD => "DEFAULT")
port map (
O => O, -- Diff_p output (connect directly to top-level port)
OB => OB, -- Diff_n output (connect directly to top-level port)
I => I, -- Buffer input
T => T -- 3-state enable input
);
-- End of OBUFTDS_inst instantiation
Verilog Instantiation Template
// OBUFTDS: Differential 3-state Output Buffer
// 7 Series
// Xilinx HDL Language Template, version 2026.1
OBUFTDS #(
.IOSTANDARD("DEFAULT"), // Specify the output I/O standard
.SLEW("SLOW") // Specify the output slew rate
) OBUFTDS_inst (
.O(O), // Diff_p output (connect directly to top-level port)
.OB(OB), // Diff_n output (connect directly to top-level port)
.I(I), // Buffer input
.T(T) // 3-state enable input
);
// End of OBUFTDS_inst instantiation
Related Information
- 7 Series FPGAs SelectIO Resources User Guide (UG471)