XC3S100E_06 Datasheet, PDF (71/231 Pages) Xilinx, Inc – Configurable Logic Block (CLB)

R
Functional Description
Table 48: Pull-up or Pull-down Values for HSWAP, M[2:0], and VS[2:0]
I/O Pull-up Resistors
HSWAP Value during Configuration
Required Resistor Value to Define Logic Level on
HSWAP, M[2:0], or VS[2:0]
High
Low
0
Enabled
Pulled High via an internal pull-up
resistor to the associated V_CCO
supply. No external pull-up
resistor is necessary.
Pulled Low using an appropriately sized
pull-down resistor to GND.
For a 2.5V or 3.3V interface: R < 560 Ω.
For a 1.8V interface: R < 1.1 kΩ.
1
Disabled
Pulled High using a 3.3 to 4.7 kΩ Pulled Low using a 3.3 to 4.7 kΩ resistor
resistor to the associated V_CCO to GND.
supply.
The logic level on HSWAP dictates how to define the logic
levels on M[2:0] and VS[2:0], as shown in Table 48. If the
application requires HSWAP to be High, the HSWAP pin is
pulled High using an external 3.3 to 4.7 kΩ resistor to
VCCO_0. If the application requires HSWAP to be Low dur-
ing configuration, then HSWAP is either connected to GND
or pulled Low using an appropriately sized external
pull-down resistor to GND. When HSWAP is Low, its pin has
an internal pull-up resistor to VCCO_0. The external
pull-down resistor must be strong enough to define a logic
Low on HSWAP for the I/O standard used during configura-
tion. For 2.5V or 3.3V I/O, the pull-down resistor is 560 Ω or
lower. For 1.8V I/O, the pull-down resistor is 1.1 kΩ or
lower.
Once HSWAP is defined, use Table 48 to define the logic
values for M[2:0] and VS[2:0].
Use the weakest external pull-up or pull-down resistor value
allowed by the application. The resistor must be strong
enough to define a logic Low or High during configuration.
However, when driving the HSWAP, M[2:0], or VS[2:0] pins
after configuration, the output driver must be strong enough
to overcome the pull-up or pull-down resistor value and
generate the appropriate logic levels. For example, to over-
come a 560 Ω pull-down resistor, a 3.3V FPGA I/O pin must
use a 6 mA or stronger driver.
DS312-2 (v3.4) November 9, 2006
www.xilinx.com
71
Product Specification