infer_diff_pairs - 2022.1 English

Vivado Design Suite Tcl Command Reference Guide (UG835)

Document ID
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2022.1 English

Infer differential pairs, typically for ports just imported from a CSV or XDC file


infer_diff_pairs [‑file_type <arg>] [‑quiet] [‑verbose] [<file>...]


Name Description
[-file_type] Input file type: 'csv' or 'xdc' Default: file type
[-quiet] Ignore command errors
[-verbose] Suspend message limits during command execution
[<file>] Pin Planning CSV or XDC file Default: file




The infer_diff_pairs command can be used in an I/O Pin Planning project, after importing the I/O pin information using the read_csv or read_xdc command.

There are several attributes that identify differential pairs in the file: Signal Name, DiffPair Signal, DiffPair Type, and I/O Standard.

The tool will identify differential pairs using the following methods:

  • Matching Diff Pair - This is a direct definition of the two signals which make up a differential pair. Two port entries, each have DiffPair Signal values linking to the Signal Name of the other, and have complementary DiffPair Type values, one N and one P. The tool checks to ensure that the other attributes such as I/O Standard are compatible when forming the diff pair.
  • Unmatched Diff Pair - Two port entries, with complementary DiffPair Type values (one N, one P), but only one port has a DiffPair Signal linking to the other Signal Name. The tool will create the differential pair if all other attributes are compatible.
  • Single Port Diff Pair - A single port entry with a differential I/O Standard, a DiffPair Type value, and a DiffPair Signal that does not otherwise appear in the CSV. The tool will create the opposite side of the differential pair (the N or P side), with all properties matching those on the original port.
  • Inferred Diff Pair - Two ports entries, with Signal Names that imply the N and P side. The tool will infer a differential pair if all other attributes are compatible.

After reading the port definitions from a CSV or XDC file, the tool will report that some differential pairs can be inferred from the data. You can run the infer_diff_pairs command to infer these differential pairs if you choose.


-file_type [ csv | xdc ] - (Optional) Specify the type of file to import when inferring differential pairs. The valid file types are CSV and XDC. There is no default; the -file_type must be specified.

-quiet - (Optional) Execute the command quietly, returning no messages from the command. The command also returns TCL_OK regardless of any errors encountered during execution.
Note: Any errors encountered on the command-line, while launching the command, will be returned. Only errors occurring inside the command will be trapped.
-verbose - (Optional) Temporarily override any message limits and return all messages from this command.
Note: Message limits can be defined with the set_msg_config command.
<file> - (Optional) The name of the file previously imported.
Note: If the path is not specified as part of the file name, the tool will search for the specified file in the current working directory and then in the directory from which the tool was launched.


The following example imports the specified XDC file, and then infers differential pairs from the file:
read_xdc C:/Vivado_Install/io_1.xdc
infer_diff_pairs C:/Vivado_Install/io_1.xdc -file_type xdc

See Also