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| Element | XC3000 | XC4000E | XC4000X | XC5200 | XC9000 | Spartan | SpartanXL | Spartan2 | Virtex |
|---|---|---|---|---|---|---|---|---|---|
| OBUF | Primitive | Primitive | Primitive | Primitive | Primitive | Primitive | Primitive | Primitive | Primitive |
| OBUF4, OBUF8, OBUF16 | Macro | Macro | Macro | Macro | Macro | Macro | Macro | Macro | Macro |
OBUF, OBUF4, OBUF8, and OBUF16 are single and multiple output buffers. 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.
For XC9000 CPLDs, if a high impedance (Z) signal from an on-chip 3-state buffer (like BUFE) is applied to the input of an OBUF, it is propagated to the CPLD device output pin.
For Virtex and Spartan2, refer to the “OBUF_selectIO” section for information on OBUF variants with selectable I/O interfaces. The I/O interface standard used by OBUF, 4, 8, and 16 is LVTTL. Also, Virtex and Spartan2 OBUF, 4, 8, and 16 have selectable drive and slew rates using the DRIVE and SLOW or FAST constraints. The defaults are DRIVE=12 mA and SLOW slew.
Figure 8.1 OBUF8 Implementation XC3000, XC4000E, XC4000X, XC5200, XC9000, Spartan, SpartanXL, Spartan2, Virtex