OBUFT_selectIO

Single 3-State Output Buffer with Active-Low Output Enable and Selectable I/O Interface

OBUFT and its variants (listed below) are single 3-state output buffers with active-Low output Enable whose I/O interface corresponds to a specific I/O standard. The name extensions (LVCMOS2, PCI33_3, PCI33_5, etc.) specify the standard. The S, F, and 2, 4, 6, 8, 12, 16, 24 extensions specify the slew rate (SLOW or FAST) and the drive power (2, 4, 6, 8, 12, 16, 24 mA) for the LVTTL standard. For example, OBUFT_S_4 is a 3-state output buffer with active-low output enable that uses the LVTTL I/O signaling standard with a SLOW slew and 4mA of drive power.

OBUFT has selectable drive and slew rates using the DRIVE and FAST or SLOW constraints. The defaults are DRIVE=12 mA and SLOW slew.

When T is Low, data on the input of the buffer is transferred to the output. When T is High, the output is high impedance (off or Z state). OBUFTs isolate the internal circuit and provide extra drive current for signals leaving a chip. An OBUFT output is connected to an OPAD or an IOPAD.

The hardware implementation of the I/O standards requires that you follow a set of usage rules for the SelectI/O buffer components. Refer to the “SelectI/O Usage Rules” section under the IBUF_selectIO section for information on using these components.