XC3S100E_06 Datasheet, PDF (19/231 Pages) Xilinx, Inc – Configurable Logic Block (CLB)

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Functional Description
These differences are outlined for each package, such as
pins that are unconnected on one device but connected on
another in the same package or pins that are dedicated
inputs on one package but full I/O on another. When design-
ing the printed circuit board (PCB), plan for potential future
upgrades and package migration.
The Spartan-3E family is not pin-compatible with any previ-
ous Xilinx FPGA family.
Dedicated Inputs
Dedicated Inputs are IOBs used only as inputs. Pin names
designate a Dedicated Input if the name starts with IP, for
example, IP or IP_Lxxx_x. Dedicated inputs retain the full
functionality of the IOB for input functions with a single
exception for differential inputs (IP_Lxxx_x). For the differ-
ential Dedicated Inputs, the on-chip differential termination
is not available. To replace the on-chip differential termina-
tion, choose a differential pair that supports outputs
(IO_Lxxx_x) or use an external 100Ω termination resistor on
the board.
ESD Protection
Clamp diodes protect all device pads against damage from
Electro-Static Discharge (ESD) as well as excessive voltage
transients. Each I/O has two clamp diodes: one diode
extends P-to-N from the pad to V_CCO and a second diode
extends N-to-P from the pad to GND. During operation,
these diodes are normally biased in the off state. These
clamp diodes are always connected to the pad, regardless
of the signal standard selected. The presence of diodes lim-
its the ability of Spartan-3E I/Os to tolerate high signal volt-
ages. The V_IN absolute maximum rating in Table 72 of DC
and Switching Characteristics (Module 3) specifies the
voltage range that I/Os can tolerate.
Supply Voltages for the IOBs
The IOBs are powered by three supplies:
1. The V_CCO supplies, one for each of the FPGA’s I/O
banks, power the output drivers. The voltage on the
V_CCO pins determines the voltage swing of the output
signal.
2. V_CCINT is the main power supply for the FPGA’s internal
logic.
3. V_CCAUX is an auxiliary source of power, primarily to
optimize the performance of various FPGA functions
such as I/O switching.
I/O and Input-Only Pin Behavior During
Power-On, Configuration, and User Mode
In this section, all behavior described for I/O pins also
applies to input-only pins and dual-purpose I/O pins that are
not actively involved in the currently-selected configuration
mode.
All I/O pins have ESD clamp diodes to their respective V_CCO
supply and from GND, as shown in Figure 5. The V_CCINT
(1.2V), V_CCAUX (2.5V), and V_CCO supplies can be applied in
any order. Before the FPGA can start its configuration pro-
cess, V_CCINT, V_CCO Bank 2, and V_CCAUX must have reached
their respective minimum recommended operating levels
indicated in Table 73. At this time, all output drivers are in a
high-impedance state. V_CCO Bank 2, V_CCINT, and V_CCAUX
serve as inputs to the internal Power-On Reset circuit
(POR).
A Low level applied to the HSWAP input enables pull-up
resistors on user-I/O and input-only pins from power-on
throughout configuration. A High level on HSWAP disables
the pull-up resistors, allowing the I/Os to float. HSWAP con-
tains a weak pull-up and defaults to High if left floating. As
soon as power is applied, the FPGA begins initializing its
configuration memory. At the same time, the FPGA inter-
nally asserts the Global Set-Reset (GSR), which asynchro-
nously resets all IOB storage elements to a default Low
state. Also see Pin Behavior During Configuration.
Upon the completion of initialization and the beginning of
configuration, INIT_B goes High, sampling the M0, M1, and
M2 inputs to determine the configuration mode. Configura-
tion data is then loaded into the FPGA. The I/O drivers
remain in a high-impedance state (with or without pull-up
resistors, as determined by the HSWAP input) throughout
configuration.
At the end of configuration, the GSR net is released, placing
the IOB registers in a Low state by default, unless the
loaded design reverses the polarity of their respective SR
inputs.
The Global Three State (GTS) net is released during
Start-Up, marking the end of configuration and the begin-
ning of design operation in the User mode. After the GTS
net is released, all user I/Os go active while all unused I/Os
DS312-2 (v3.4) November 9, 2006
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Product Specification