R
Virtex-II Platform FPGAs: Functional Description
Table 4:
LVTTL and LVCMOS Programmable Currents (Sink and Source)
SelectI/O-Ultra
LVTTL
LVCMOS33
LVCMOS25
LVCMOS18
LVCMOS15
2 mA
2 mA
2 mA
2 mA
2 mA
Programmable Current (Worst-Case Guaranteed Minimum)
4 mA
4 mA
4 mA
4 mA
4 mA
6 mA
6 mA
6 mA
6 mA
6 mA
8 mA
8 mA
8 mA
8 mA
8 mA
12 mA
12 mA
12 mA
12 mA
12 mA
16 mA
16 mA
16 mA
16 mA
16 mA
24 mA
24 mA
24 mA
n/a
n/a
shows the SSTL2, SSTL3, and HSTL configura-
tions. HSTL can sink current up to 48 mA. (HSTL IV)
VCCO
OBUF
Clamp
Diode
Input Path
The Virtex-II IOB input path routes input signals directly to
internal logic and / or through an optional input flip-flop or
latch, or through the DDR input registers. An optional delay
element at the D-input of the storage element eliminates
pad-to-pad hold time. The delay is matched to the internal
clock-distribution delay of the Virtex-II device, and when
used, assures that the pad-to-pad hold time is zero.
Each input buffer can be configured to conform to any of the
low-voltage signaling standards supported. In some of
these standards the input buffer utilizes a user-supplied
threshold voltage, V
REF
. The need to supply V
REF
imposes
constraints on which standards can be used in the same
bank. See I/O banking description.
PAD
Output Path
VREF
VCCAUX = 3.3V
VCCINT = 1.5V
DS031_24_100900
Figure 6:
SSTL or HSTL SelectI/O-Ultra Standards
All pads are protected against damage from electrostatic
discharge (ESD) and from over-voltage transients. Virtex-II
uses two memory cells to control the configuration of an I/O
as an input. This is to reduce the probability of an I/O con-
figured as an input from flipping to an output when sub-
jected to a single event upset (SEU) in space applications.
Prior to configuration, all outputs not involved in configura-
tion are forced into their high-impedance state. The
pull-down resistors and the weak-keeper circuits are inac-
tive. The dedicated pin HSWAP_EN controls the pull-up
resistors prior to configuration. By default, HSWAP_EN is
set high, which disables the pull-up resistors on user I/O
pins. When HSWAP_EN is set low, the pull-up resistors are
activated on user I/O pins.
All Virtex-II IOBs support IEEE 1149.1 compatible Bound-
ary-Scan testing.
The output path includes a 3-state output buffer that drives
the output signal onto the pad. The output and / or the
3-state signal can be routed to the buffer directly from the
internal logic or through an output / 3-state flip-flop or latch,
or through the DDR output / 3-state registers.
Each output driver can be individually programmed for a
wide range of low-voltage signaling standards. In most sig-
naling standards, the output High voltage depends on an
externally supplied V
CCO
voltage. The need to supply V
CCO
imposes constraints on which standards can be used in the
same bank. See I/O banking description.
I/O Banking
Some of the I/O standards described above require V
CCO
and V
REF
voltages. These voltages are externally supplied
and connected to device pins that serve groups of IOB
blocks, called banks. Consequently, restrictions exist about
which I/O standards can be combined within a given bank.
Eight I/O banks result from dividing each edge of the FPGA
into two banks, as shown in
and
Each
bank has multiple V
CCO
pins, all of which must be con-
nected to the same voltage. This voltage is determined by
the output standards in use.
DS031-2 (v3.5) November 5, 2007
Product Specification
Module 2 of 4
5
XILINX [ XILINX, INC ]
