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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 |
OBUF and its variants (listed below) are single output 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, OBUF_F_12 is a single output buffer that uses the LVTTL I/O-signaling standard with a FAST slew and 12mA of drive power.
OBUF has selectable drive and slew rates using the DRIVE and SLOW or FAST constraints. The defaults are DRIVE=12 mA and SLOW slew.
An OBUF isolates the internal circuit and provides drive current for signals leaving a chip. OBUFs exist in input/output blocks (IOB). The output (O) of an OBUF is connected to an OPAD or an IOPAD.
The hardware implementation of the I/O standard 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 |
|---|---|---|
| OBUF | LVTTL | 3.3 |
| OBUF_S_2 | LVTTL | 3.3 |
| OBUF_S_4 | LVTTL | 3.3 |
| OBUF_S_6 | LVTTL | 3.3 |
| OBUF_S_8 | LVTTL | 3.3 |
| OBUF_S_12 | LVTTL | 3.3 |
| OBUF_S_16 | LVTTL | 3.3 |
| OBUF_S_24 | LVTTL | 3.3 |
| OBUF_F_2 | LVTTL | 3.3 |
| OBUF_F_4 | LVTTL | 3.3 |
| OBUF_F_6 | LVTTL | 3.3 |
| OBUF_F_8 | LVTTL | 3.3 |
| OBUF_F_12 | LVTTL | 3.3 |
| OBUF_F_16 | LVTTL | 3.3 |
| OBUF_F_24 | LVTTL | 3.3 |
| OBUF_LVCMOS2 | LVCMOS2 | 2.5 |
| OBUF_PCI33_3 | PCI33_3 | 3.3 |
| OBUF_PCI33_5 | PCI33_5 | 3.3 |
| OBUF_PCI66_3 | PCI66_3 | 3.3 |
| OBUF_GTL | GTL | N/A |
| OBUF_GTLP | GTL+ | N/A |
| OBUF_HSTL_I | HSTL_I | 1.5 |
| OBUF_HSTL_III | HSTL_III | 1.5 |
| OBUF_HSTL_IV | HSTL_IV | 1.5 |
| OBUF_SSTL2_I | SSTL2_I | 2.5 |
| OBUF_SSTL2_II | SSTL2_II | 2.5 |
| OBUF_SSTL3_I | SSTL3_I | 3.3 |
| OBUF_SSTL3_II | SSTL3_II | 3.3 |
| OBUF_CTT | CTT | 3.3 |
| OBUF_AGP | AGP | 3.3 |