XC2S50 Xilinx, Inc., XC2S50 Datasheet - Page 41

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

Spartan-II 2.5V FPGA Family: Functional Description
<slew_rate> can be 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 OBUFT symbol.
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The Versatile I/O OBUFT placement restrictions require that
within a given V
put source drive voltage. Input buffers of any type and out-
put buffers that do not require V
the same V
Module 2 of 4
34
Figure 38: 3-State Output Buffer Symbol (OBUFT
OBUFT
OBUFT_S_2
OBUFT_S_4
OBUFT_S_6
OBUFT_S_8
OBUFT_S_12
OBUFT_S_16
OBUFT_S_24
OBUFT_F_2
OBUFT_F_4
OBUFT_F_6
OBUFT_F_8
OBUFT_F_12
OBUFT_F_16
OBUFT_F_24
OBUFT_LVCMOS2
OBUFT_PCI33_3
OBUFT_PCI33_5
OBUFT_PCI66_3
OBUFT_GTL
OBUFT_GTLP
OBUFT_HSTL_I
OBUFT_HSTL_III
OBUFT_HSTL_IV
OBUFT_SSTL3_I
OBUFT_SSTL3_II
OBUFT_SSTL2_I
OBUFT_SSTL2_II
OBUFT_CTT
OBUFT_AGP
CCO
CCO
bank.
bank each OBUFT share the same out-
T
I
IOBUFT
DS001_39_032300
CCO
IO
can be placed within
www.xilinx.com
1-800-255-7778
The LOC property can specify a location for the OBUFT.
3-state output buffers and bidirectional buffers can have
either a weak pull-up resistor, a weak pull-down resistor, or
a weak "keeper" circuit. Control this feature by adding the
appropriate symbol to the output net of the OBUFT
(PULLUP, PULLDOWN, or KEEPER).
The weak "keeper" circuit requires the input buffer within the
IOB to sample the I/O signal. So, OBUFTs programmed for
an I/O standard that requires a V
ment of a V
a weak "keeper" circuit. This restriction does not affect most
circuit design as applications using an OBUFT configured
with a weak "keeper" typically implement a bidirectional I/O.
In this case the IBUF (and the corresponding V
explicitly placed.
The LOC property can specify a location for the OBUFT.
IOBUF
Use the IOBUF symbol for bidirectional signals that require
both an input buffer and a 3-state output buffer with an
active high 3-state pin. The generic input/output buffer
IOBUF appears in
The extension to the base name defines which I/O standard
the IOBUF uses. With no extension specified for the generic
IOBUF symbol, the assumed standard is LVTTL input buffer
and slew rate limited LVTTL with 12 mA drive strength for
the output buffer.
The LVTTL IOBUF 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 bidirectional buffers have selectable output drive
strengths.
The format for LVTTL IOBUF symbol names is as follows:
<slew_rate> can be either F (Fast), or S (Slow) and
<drive_strength> is specified in milliamps (2, 4, 6, 8, 12, 16,
or 24).
Figure 39: Input/Output Buffer Symbol (IOBUF)
IOBUF_<slew_rate>_<drive_strength>
REF
in the bank with an OBUFT configured with
Figure
T
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I
39.
DS001-2 (v2.2) September 3, 2003
IOBUF
DS001_40_061200
REF
IO
have automatic place-
Product Specification
REF
) are
R