Primitive: Differential Signaling Output Buffer
Introduction
This design element is a single
output buffer that supports low-voltage, differential signaling. OBUFDS
isolates the internal circuit and provides drive current for signals
leaving the chip. Its output is represented as two distinct ports
(O and OB), one deemed the "master" and the other the "slave." The
master and the slave are opposite phases of the same logical signal
(for example, MYNET and MYNETB).
Logic Table
| Inputs |
Outputs |
| I |
O |
OB |
| 0 |
0 |
1 |
| 1 |
1 |
0 |
Port Descriptions
| Port |
Direction |
Width |
Function |
| O |
Output |
1 |
Diff_p output (connect directly to top level port). |
| OB |
Output |
1 |
Diff_n output (connect directly to top level port). |
| I |
Input |
1 |
Buffer input. |
Design Entry Method
| Instantiation |
Recommended |
| Inference |
No |
| IP Catalog |
No |
| Macro support |
No |
Available Attributes
| Attribute |
Type |
Allowed Values |
Default |
Description |
| IOSTANDARD |
STRING |
See Data Sheet |
"DEFAULT" |
Assigns an I/O standard to the element. |
| SLEW |
STRING |
"SLOW" or "FAST" |
"SLOW" |
Specifies the slew rate of the output driver. Consult the product
Data Sheet for recommendations of the best setting for this attribute. |
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;
-- OBUFDS: Differential Output Buffer
-- 7 Series
-- Xilinx HDL Language Template, version 2021.2
OBUFDS_inst : OBUFDS
generic map (
IOSTANDARD => "DEFAULT", -- Specify the output I/O standard
SLEW => "SLOW") -- Specify the output slew rate
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
);
-- End of OBUFDS_inst instantiation
Verilog
Instantiation Template
// OBUFDS: Differential Output Buffer
// 7 Series
// Xilinx HDL Language Template, version 2021.2
OBUFDS #(
.IOSTANDARD("DEFAULT"), // Specify the output I/O standard
.SLEW("SLOW") // Specify the output slew rate
) OBUFDS_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
);
// End of OBUFDS_inst instantiation
