R
Spartan and Spartan-XL Families Field Programmable Gate Arrays
The register choice is made by placing the appropriate
library symbol. For example, IFD is the basic input flip-flop
(rising edge triggered), and ILD is the basic input latch
(transparent-High). Variations with inverted clocks are also
available. The clock signal inverter is also shown in Figure 5
on the CK line.
The 5V Spartan input buffers can be globally configured for
either TTL (1.2V) or CMOS (VCC/2) thresholds, using an
option in the bitstream generation software. The Spartan
output levels are also configurable; the two global adjust-
ments of input threshold and output level are independent.
The inputs of Spartan devices can be driven by the outputs
of any 3.3V device, if the Spartan inputs are in TTL mode.
Input and output thresholds are TTL on all configuration
pins until the configuration has been loaded into the device
and specifies how they are to be used. Spartan-XL inputs
are TTL compatible and 3.3V CMOS compatible.
The Spartan IOB data input path has a one-tap delay ele-
ment: either the delay is inserted (default), or it is not. The
Spartan-XL IOB data input path has a two-tap delay ele-
ment, with choices of a full delay, a partial delay, or no delay.
The added delay guarantees a zero hold time with respect
to clocks routed through the global clock buffers. (See Glo-
bal Nets and Buffers, page 12 for a description of the glo-
bal clock buffers in the Spartan/XL families.) For a shorter
input register setup time, with positive hold-time, attach a
NODELAY attribute or property to the flip-flop.The output of
the input register goes to the routing channels (via I1 and I2
in Figure 6). The I1 and I2 signals that exit the IOB can each
carry either the direct or registered input signal.
Supported sources for Spartan/XL device inputs are shown
in Table 4.
Spartan-XL I/Os are fully 5V tolerant even though the V is
CC
3.3V. This allows 5V signals to directly connect to the Spar-
tan-XL inputs without damage, as shown in Table 4. In addi-
tion, the 3.3V V can be applied before or after 5V signals
CC
are applied to the I/Os. This makes the Spartan-XL devices
immune to power supply sequencing problems.
GTS
T
D
Q
O
OUTPUT DRIVER
Programmable Slew Rate
Programmable TTL/CMOS Drive
(Spartan only)
CK
EC
OK
Package
Pad
I1
I2
INPUT BUFFER
Delay
D
Q
Programmable
Pull-Up/
Pull-Down
Network
IK
CK
EC
Multiplexer Controlled
by Configuration Program
EC
DS060_06_041901
Figure 6: Simplified Spartan/XL IOB Block Diagram
DS060 (v1.6) September 19, 2001
www.xilinx.com
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Product Specification
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