Spartan-IIE FPGA Family: Functional Description
is required for most output standards and for LVTTL,
LVCMOS, and PCI inputs.
Table 4:
Compatible Standards
V
CCO
3.3V
2.5V
1.8V
1.5V
Compatible Standards
PCI, LVTTL, SSTL3 I, SSTL3 II, CTT, AGP,
LVPECL, GTL, GTL+
SSTL2 I, SSTL2 II, LVCMOS2, LVDS, Bus
LVDS, GTL, GTL+
LVCMOS18, GTL, GTL+
HSTL I, HSTL III, HSTL IV, GTL, GTL+
R
Hot Swap, Hot Insertion, Hot Socketing Support
The I/O pins support hot swap — also called hot insertion
and hot socketing — and are considered CompactPCI
Friendly according to the PCI Bus v2.2 Specification. Con-
sequently, an unpowered Spartan-IIE FPGA can be
plugged directly into a powered system or backplane with-
out affecting or damaging the system or the FPGA. The hot
swap functionality is built into every XC2S150E,
XC2S400E, and XC2S600E device. All other Spartan-IIE
devices built after Product Change Notice
also
include hot swap functionality.
To support hot swap, Spartan-IIE devices include the follow-
ing I/O features.
•
Signals can be applied to Spartan-IIE FPGA I/O pins
before powering the FPGA’s V
CCINT
or V
CCO
supply
inputs.
Spartan-IIE FPGA I/O pins are high-impedance (i.e.,
three-stated) before and throughout the power-up and
configuration processes when employing a
configuration mode that does not enable the
preconfiguration weak pull-up resistors (see
There is no current path from the I/O pin back to the
V
CCINT
or V
CCO
voltage supplies.
Spartan-IIE FPGAs are immune to latch-up during hot
swap.
Some input standards require a user-supplied threshold
voltage, V
REF
. In this case, certain user-I/O pins are auto-
matically configured as inputs for the V
REF
voltage. About
one in six of the I/O pins in the bank assume this role.
V
REF
pins within a bank are interconnected internally and
consequently only one V
REF
voltage can be used within
each bank. All V
REF
pins in the bank, however, must be con-
nected to the external voltage source for correct operation.
In a bank, inputs requiring V
REF
can be mixed with those
that do not but only one V
REF
voltage may be used within a
bank. The V
CCO
and V
REF
pins for each bank appear in the
device pinout tables.
Within a given package, the number of V
REF
and V
CCO
pins
can vary depending on the size of device. In larger devices,
more I/O pins convert to V
REF
pins. Since these are always
a superset of the V
REF
pins used for smaller devices, it is
possible to design a PCB that permits migration to a larger
device. All V
REF
pins for the largest device anticipated must
be connected to the V
REF
voltage, and not used for I/O.
Table 5:
I/O Banking
Package
V
CCO
Banks
V
REF
Banks
TQ144, PQ208
Interconnected as 1
8 independent
FT256, FG456,
FG676
8 independent
8 independent
•
•
•
Once connected to the system, each pin adds a small
amount of capacitance (C
IN
). Likewise, each I/O consumes
a small amount of DC current, equivalent to the input leak-
age specification (I
L
). There also may be a small amount of
temporary AC current (I
HSPO
) when the pin input voltage
exceeds V
CCO
plus 0.4V, which lasts less than 10 ns.
A weak-keeper circuit within each user-I/O pin is enabled
during the last frame of configuration data and has no
noticeable effect on robust system signals driven by an
active driver or a strong pull-up or pull-down resistor.
Undriven or floating system signals may be affected. The
specific effect depends on how the I/O pin is configured.
User-I/O pins configured as outputs or enabled outputs
have a weak pull-up resistor to V
CCO
during the last config-
uration frame. User-I/O pins configured as inputs or bidirec-
tional I/Os have weak pull-down resistors. The weak-keeper
circuit turns off when the DONE pin goes High, provided
that it is not used in the configured application.
See Xilinx
®
Application Note
for more information
on I/O resources.
12
DS077-2 (v2.3) June 18, 2008
Product Specification
XILINX [ XILINX, INC ]
