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| XC3000 | XC4000E | XC4000X | XC5200 | XC9000 | Spartan | SpartanXL | Spartan2 | Virtex |
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| N/A | N/A | N/A | N/A | N/A | N/A | N/A | Primitive | Primitive |
IOBUF and its variants (listed below) are bi-directional buffers 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 variants. For example, IOBUF_F_2 is a bi-directional buffer that uses the LVTTL I/O-signaling standard with a FAST slew and 2mA of drive power.
IOBUF (LVTTL) has selectable drive and slew rates using the DRIVE and FAST or SLOW constraints. The defaults are DRIVE=12 mA and SLOW slew.
IOBUFs are composites of IBUF and OBUFT elements. The O output is X (unknown) when IO (input/output) is Z. IOBUFs can be implemented as interconnections of their component elements.
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.
| Component | I/O Standard | VCCO | VREF |
|---|---|---|---|
| IOBUF | LVTTL | 3.3 | N/A |
| IOBUF_S_2 | LVTTL | 3.3 | N/A |
| IOBUF_S_4 | LVTTL | 3.3 | N/A |
| IOBUF_S_6 | LVTTL | 3.3 | N/A |
| IOBUF_S_8 | LVTTL | 3.3 | N/A |
| IOBUF_S_12 | LVTTL | 3.3 | N/A |
| IOBUF_S_16 | LVTTL | 3.3 | N/A |
| IOBUF_S_24 | LVTTL | 3.3 | N/A |
| IOBUF_F_2 | LVTTL | 3.3 | N/A |
| IOBUF_F_4 | LVTTL | 3.3 | N/A |
| IOBUF_F_6 | LVTTL | 3.3 | N/A |
| IOBUF_F_8 | LVTTL | 3.3 | N/A |
| IOBUF_F_12 | LVTTL | 3.3 | N/A |
| IOBUF_F_16 | LVTTL | 3.3 | N/A |
| IOBUF_F_24 | LVTTL | 3.3 | N/A |
| IOBUF_LVCMOS2 | LVCMOS2 | 2.5 | N/A |
| IOBUF_PCI33_3 | PCI33_3 | 3.3 | N/A |
| IOBUF_PCI33_5 | PCI33_5 | 3.3 | N/A |
| IOBUF_PCI66_3 | PCI66_3 | 3.3 | N/A |
| IOBUF_GTL | GTL | N/A | 0.80 |
| IOBUF_GTLP | GTL+ | N/A | 1.00 |
| IOBUF_HSTL_I | HSTL_I | 1.5 | 0.75 |
| IOBUF_HSTL_III | HSTL_III | 1.5 | 0.90 |
| IOBUF_HSTL_IV | HSTL_IV | 1.5 | 0.75 |
| IOBUF_SSTL2_I | SSTL2_I | 2.5 | 1.10 |
| IOBUF_SSTL2_II | SSTL2_II | 2.5 | 1.10 |
| IOBUF_SSTL3_I | SSTL3_I | 3.3 | 0.90 |
| IOBUF_SSTL3_II | SSTL3_II | 3.3 | 1.50 |
| IOBUF_CTT | CTT | 3.3 | 1.50 |
| IOBUF_AGP | AGP | 3.3 | 1.32 |