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OBUFT_selectIO

Single 3-State Output Buffer with Active-Low Output Enable and 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/x8720.gif

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.

Inputs
Outputs
T
I
O
1
X
Z
0
1
1
0
0
0

Component
I/O Standard
VCCO
OBUFT
LVTTL
3.3
OBUFT_S_2
LVTTL
3.3
OBUFT_S_4
LVTTL
3.3
OBUFT_S_6
LVTTL
3.3
OBUFT_S_8
LVTTL
3.3
OBUFT_S_12
LVTTL
3.3
OBUFT_S_16
LVTTL
3.3
OBUFT_S_24
LVTTL
3.3
OBUFT_F_2
LVTTL
3.3
OBUFT_F_4
LVTTL
3.3
OBUFT_F_6
LVTTL
3.3
OBUFT_F_8
LVTTL
3.3
OBUFT_F_12
LVTTL
3.3
OBUFT_F_16
LVTTL
3.3
OBUFT_F_24
LVTTL
3.3
OBUFT_LVCMOS2
LVCMOS2
2.5
OBUFT_PCI33_3
PCI33_3
3.3
OBUFT_PCI33_5
PCI33_5
3.3
OBUFT_PCI66_3
PCI66_3
3.3
OBUFT_GTL
GTL
N/A
OBUFT_GTLP
GTL+
N/A
OBUFT_HSTL_I
HSTL_I
1.5
OBUFT_HSTL_III
HSTL_III
1.5
OBUF_HSTL_IV
HSTL_IV
1.5
OBUFT_SSTL2_I
SSTL2_I
2.5
OBUFT_SSTL2_II
SSTL2_II
2.5
OBUFT_SSTL3_I
SSTL3_I
3.3
OBUFT_SSTL3_II
SSTL3_II
3.3
OBUFT_CTT
CTT
3.3
OBUFT_AGP
AGP
3.3

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