XC2S50 Xilinx, Inc., XC2S50 Datasheet - Page 40

• Manufacturer Part Number: XC2S50
• Description: Spartan-II 2.5V FPGA Family
• Manufacturer: Xilinx, Inc.

OBUF
An OBUF must drive outputs through an external output
port. The generic output buffer (OBUF) symbol appears in
Figure
The extension to the base name defines which I/O standard
the OBUF uses. With no extension specified for the generic
OBUF symbol, the assumed standard is slew rate limited
LVTTL with 12 mA drive strength.
The LVTTL OBUF additionally can support one of two slew
rate modes to minimize bus transients. By default, the slew
rate for each output buffer is reduced to minimize power bus
transients when switching non-critical signals.
LVTTL output buffers have selectable drive strengths.
The format for LVTTL OBUF symbol names is as follows.
<slew_rate> is either F (Fast), or S (Slow) and
<drive_strength> is specified in milliamps (2, 4, 6, 8, 12, 16,
or 24).
The following list details variations of the OBUF symbol.
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DS001-2 (v2.2) September 3, 2003
Product Specification
OBUF
OBUF_S_2
OBUF_S_4
OBUF_S_6
OBUF_S_8
OBUF_S_12
OBUF_S_16
OBUF_S_24
OBUF_F_2
OBUF_F_4
OBUF_F_6
OBUF_F_8
OBUF_F_12
OBUF_F_16
OBUF_F_24
OBUF_LVCMOS2
OBUF_PCI33_3
OBUF_PCI33_5
OBUF_PCI66_3
37.
Figure 37: Output Buffer (OBUF) Symbol
OBUF_<slew_rate>_<drive_strength>
R
I
OBUF
DS001_38_061200
O
www.xilinx.com
1-800-255-7778
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OBUF placement restrictions require that within a given
V
voltage. Input buffers of any type and output buffers that do
not require V
Table 16
The LOC property can specify a location for the OBUF.
Table 16: Output Standards Compatibility
Requirements
OBUFT
The generic 3-state output buffer OBUFT, shown in
Figure
tional I/O.
The extension to the base name defines which I/O standard
OBUFT uses. With no extension specified for the generic
OBUFT symbol, the assumed standard is slew rate limited
LVTTL with 12 mA drive strength.
The LVTTL OBUFT additionally can support one of two slew
rate modes to minimize bus transients. By default, the slew
rate for each output buffer is reduced to minimize power bus
transients when switching non-critical signals.
LVTTL 3-state output buffers have selectable drive
strengths.
The format for LVTTL OBUFT symbol names is as follows.
CCO
Rule 1
Rule 2
V
Spartan-II 2.5V FPGA Family: Functional Description
3.3
2.5
1.5
CCO
OBUF_GTL
OBUF_GTLP
OBUF_HSTL_I
OBUF_HSTL_III
OBUF_HSTL_IV
OBUF_SSTL3_I
OBUF_SSTL3_II
OBUF_SSTL2_I
OBUF_SSTL2_II
OBUF_CTT
OBUF_AGP
bank each OBUF share the same output source drive
38, typically implements 3-state outputs or bidirec-
summarizes the output compatibility requirements.
OBUFT_<slew_rate>_<drive_strength>
Only outputs with standards which share
compatible V
bank.
There are no placement restrictions for outputs
with standards that do not require a V
Compatible Standards
LVTTL, SSTL3_I, SSTL3_II, CTT, AGP, GTL,
GTL+, PCI33_3, PCI66_3
SSTL2_I, SSTL2_II, LVCMOS2, GTL, GTL+
HSTL_I, HSTL_III, HSTL_IV, GTL, GTL+
CCO
can be placed within any V
CCO
may be used within the same
Module 2 of 4
CCO
CCO
.
bank.
33