|
XC4013E-3PQ160I Datasheet, PDF (35/68 Pages) Xilinx, Inc – XC4000E and XC4000X Series Field Programmable Gate Arrays | |||
|
◁ |
Product Obsolete or Under Obsolescence
R
XC4000E and XC4000X Series Field Programmable Gate Arrays
The top and bottom Global Early buffers are about 1 ns
slower clock to out than the left and right Global Early buff-
ers.
The Global Early buffers can be driven by either semi-ded-
icated pads or internal logic. They share pads with the Glo-
bal Low-Skew buffers, so a single net can drive both global
buffers, as described above.
GND
Ground and
Vcc Ring for
I/O Drivers
To use a Global Early buffer, place a BUFGE element in a
schematic or in HDL code. If desired, attach a LOC
attribute or property to direct placement to the designated
location. For example, attach a LOC=T attribute or property
to direct that a BUFGE be placed in one of the two Global
Early buffers on the top edge of the device, or a LOC=TR to
indicate the Global Early buffer on the top edge of the
device, on the right.
Power Distribution
Vcc
Vcc
Logic
Power Grid
GND
X5422
Figure 39: XC4000 Series Power Distribution
Power for the FPGA is distributed through a grid to achieve Pin Descriptions
high noise immunity and isolation between logic and I/O.
Inside the FPGA, a dedicated Vcc and Ground ring sur-
rounding the logic array provides power to the I/O drivers,
There are three types of pins in the XC4000 Series
devices:
as shown in Figure 39. An independent matrix of Vcc and ⢠Permanently dedicated pins
Ground lines supplies the interior logic of the device.
⢠User I/O pins that can have special functions
6
This power distribution grid provides a stable supply and ⢠Unrestricted user-programmable I/O pins.
ground for all internal logic, providing the external package Before and during conï¬guration, all outputs not used for the
power pins are all connected and appropriately de-coupled. conï¬guration process are 3-stated with a 50 k⦠- 100 kâ¦
Typically, a 0.1 µF capacitor connected between each Vcc pull-up resistor.
pin and the boardâs Ground plane will provide adequate
de-coupling.
After conï¬guration, if an IOB is unused it is conï¬gured as
an input with a 50 k⦠- 100 k⦠pull-up resistor.
Output buffers capable of driving/sinking the speciï¬ed 12
mA loads under speciï¬ed worst-case conditions may be
capable of driving/sinking up to 10 times as much current
under best case conditions.
XC4000 Series devices have no dedicated Reset input.
Any user I/O can be conï¬gured to drive the Global
Set/Reset net, GSR. See âGlobal Set/Resetâ on page 11
for more information on GSR.
Noise can be reduced by minimizing external load capaci-
tance and reducing simultaneous output transitions in the
same direction. It may also be beneï¬cial to locate heavily
loaded output buffers near the Ground pads. The I/O Block
output buffers have a slew-rate limited mode (default) which
should be used where output rise and fall times are not
speed-critical.
XC4000 Series devices have no Powerdown control input,
as the XC3000 and XC2000 families do. The
XC3000/XC2000 Powerdown control also 3-stated all of the
device
I/O pins. For XC4000 Series devices, use the global 3-state
net, GTS, instead. This net 3-states all outputs, but does
not place the device in low-power mode. See âIOB Output
Signalsâ on page 23 for more information on GTS.
Device pins for XC4000 Series devices are described in
Table 16. Pin functions during conï¬guration for each of the
seven conï¬guration modes are summarized in Table 22 on
page 58, in the âConï¬guration Timingâ section.
May 14, 1999 (Version 1.6)
6-39
|
▷ |