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OBUF_selectIO

Single Output Buffer with Selectable I/O Interface

XC3000
XC4000E
XC4000X
XC5200
XC9000
Spartan
SpartanXL
Virtex
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Primitive

figures/x3830n.gif

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

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