XC3S100E Xilinx Corp., XC3S100E Datasheet - Page 18

• Manufacturer Part Number: XC3S100E
• Description: Spartan-3e Fpga Family Complete Data Sheet
• Manufacturer: Xilinx Corp.

Functional Description
Differential pairs can be shown in the Pin and Area Con-
straints Editor (PACE) with the “Show Differential Pairs”
option. A unique L-number, part of the pin name, identifies
the line-pairs associated with each bank (see
Descriptions
N designate the true and inverted lines, respectively. For
example, the pin names IO_L43P_3 and IO_L43N_3 indi-
cate the true and inverted lines comprising the line pair L43
on Bank 3.
V
ers the On-Chip Differential Termination. V
2.5V when using the On-Chip Differential Termination. The
V
To further understand how to combine multiple IOSTAN-
DARDs within a bank, refer to
page
On-Chip Differential Termination
Spartan-3E devices provide an on-chip ~120Ω differential
termination across the input differential receiver terminals.
The on-chip input differential termination in Spartan-3E
devices potentially eliminates the external 100Ω termination
resistor commonly found in differential receiver circuits. Dif-
ferential termination is used for LVDS, mini-LVDS, and
RSDS as applications permit.
On-chip Differential Termination is available in banks with
V
Set the DIFF_TERM attribute to TRUE to enable Differential
Termination on a differential I/O pin pair.
The DIFF_TERM attribute uses the following syntax in the
UCF file:
Pull-Up and Pull-Down Resistors
Pull-up and pull-down resistors inside each IOB optionally
force a floating I/O or Input-only pin to a determined state.
18
CCO
REF
CCO
Spartan-3E
Differential
Spartan-3E
Differential
INST <I/O_BUFFER_INSTANTIATION_NAME>
DIFF_TERM = “<TRUE/FALSE>”;
Output
Output
19.
lines are not required for differential operation.
provides current to the outputs and additionally pow-
= 2.5V and is not supported on dedicated input pins.
Figure 11: Differential Inputs and Outputs
in Module 4). For each pair, the letters P and
Z 0 = 50Ω
Z 0 = 50Ω
Z 0 = 50Ω
Z 0 = 50Ω
IOBs Organized into Banks,
Differential Input
Differential Input
with On-Chip
CCO
Spartan-3E
Spartan-3E
Differential
Terminator
DS312-2_24_082605
must be
Pinout
www.xilinx.com
Pull-up and pull-down resistors are commonly applied to
unused I/Os, inputs, and three-state outputs, but can be
used on any I/O or Input-only pin. The pull-up resistor con-
nects an IOB to V
value depends on the V
ing Characteristics
pull-down resistor similarly connects an IOB to ground with
a resistor. The PULLUP and PULLDOWN attributes and
library primitives turn on these optional resistors.
By default, PULLDOWN resistors terminate all unused I/O
and Input-only pins. Unused I/O and Input-only pins can
alternatively be set to PULLUP or FLOAT. To change the
unused I/O Pad setting, set the Bitstream Generator (Bit-
Gen) option
FLOAT. The UnusedPin option is accessed through the
Properties for Generate Programming File in ISE. See
stream Generator (BitGen)
During configuration a Low logic level on the HSWAP pin
activates pull-up resistors on all I/O and Input-only pins not
actively used in the selected configuration mode.
Keeper Circuit
Each I/O has an optional keeper circuit (see
keeps bus lines from floating when not being actively
driven. The
line after all drivers have been turned off. Apply the
KEEPER attribute or use the KEEPER library primitive to
use the KEEPER circuitry. Pull-up and pull-down resistors
override the KEEPER settings.
Slew Rate Control and Drive Strength
Each IOB has a slew-rate control that sets the output
switching edge-rate for LVCMOS and LVTTL outputs. The
SLEW attribute controls the slew rate and can either be set
to SLOW (default) or FAST.
Each LVCMOS and LVTTL output additionally supports up
to six different drive current strengths as shown in
To adjust the drive strength for each output, the DRIVE
attribute is set to the desired drive strength: 2, 4, 6, 8, 12,
and 16. Unless otherwise specified in the FPGA application,
the software default IOSTANDARD is LVCMOS25, SLOW
slew rate, and 12 mA output drive.
Output Path
Input Path
KEEPER
UnusedPin
Figure 12: Keeper Circuit
CCO
in Module 3 for the specifications). The
circuit retains the last logic level on a
through a resistor. The resistance
CCO
Keeper
to PULLUP, PULLDOWN, or
voltage (see
Options.
DS312-2 (v3.6) May 29, 2007
Product Specification
Pull-up
Pull-down
DS312-2_25_020807
DC and Switch-
Figure
Table
12) that
Bit-
8.
R