xa6slx9 Xilinx Corp., xa6slx9 Datasheet - Page 7

• Manufacturer Part Number: xa6slx9
• Description: Xa Spartan-6 Automotive Fpga Family
• Manufacturer: Xilinx Corp.

XA Spartan-6 Automotive FPGA Family Overview
ISERDES and OSERDES
Many applications combine high-speed bit-serial I/O with slower parallel operation inside the device. This requires a
serializer and deserializer (SerDes) inside the I/O structure. Each input has access to its own deserializer (serial-to-parallel
converter) with programmable parallel width of 2, 3, or 4 bits. Where differential inputs are used, the two serializers can be
cascaded to provide parallel widths of 5, 6, 7, or 8 bits. Each output has access to its own serializer (parallel-to-serial
converter) with programmable parallel width of 2, 3, or 4 bits. Two serializers can be cascaded when a differential driver is
used to give access to bus widths of 5, 6, 7, or 8 bits.
When distributing a double data rate clock, all SerDes data is actually clocked in/out at single data rate to eliminate the
possibility of bit errors due to duty cycle distortion. This faster single data rate clock is either derived via frequency
multiplication in a PLL, or doubled locally in each IOB by differentiating both clock edges when the incoming clock uses
double data rate.
Low-Power Gigabit Transceiver
Ultra-fast data transmission between ICs, over the backplane, or over longer distances is becoming increasingly popular and
important. It requires specialized dedicated on-chip circuitry and differential I/O capable of coping with the signal integrity
issues at these high data rates.
All XA Spartan-6 LXT devices have 2–4 gigabit transceiver circuits. Each GTP transceiver is a combined transmitter and
receiver capable of operating at a data rate between 622 Mb/s and 3.125 Gb/s. The transmitter and receiver are
independent circuits that use separate PLLs to multiply the reference frequency input by certain programmable numbers
between 2 and 25, to become the bit-serial data clock. Each GTP transceiver has a large number of user-definable features
and parameters. All of these can be defined during device configuration, and many can also be modified during operation.
Transmitter
The transmitter is fundamentally a parallel-to-serial converter with a conversion ratio of 8, 10, 16, or 20. The transmitter
output drives the PC board with a single-channel differential current-mode logic (CML) output signal.
TXOUTCLK is the appropriately divided serial data clock and can be used directly to register the parallel data coming from
the internal logic. The incoming parallel data is fed through a small FIFO and can optionally be modified with the 8B/10B
algorithm to guarantee a sufficient number of transitions. The bit-serial output signal drives two package pins with
complementary CML signals. This output signal pair has programmable signal swing as well as programmable pre-
emphasis to compensate for PC board losses and other interconnect characteristics.
Receiver
The receiver is fundamentally a serial-to-parallel converter, changing the incoming bit serial differential signal into a parallel
stream of words, each 8, 10, 16, or 20 bits wide. The receiver takes the incoming differential data stream, feeds it through a
programmable equalizer (to compensate for the PC board and other interconnect characteristics), and uses the F
input
REF
to initiate clock recognition. There is no need for a separate clock line. The data pattern uses non-return-to-zero (NRZ)
encoding and optionally guarantees sufficient data transitions by using the 8B/10B encoding scheme. Parallel data is then
transferred into the FPGA logic using the RXUSRCLK clock. The serial-to-parallel conversion ratio can be 8, 10, 16, or 20.
Integrated Endpoint Blocks for PCI Express Designs
The PCI Express standard is a packet-based, point-to-point serial interface standard. The differential signal transmission
uses an embedded clock, which eliminates the clock-to-data skew problems of traditional wide parallel buses.
The PCI Express Base Specification 1.1 defines bit rate of 2.5 Gb/s per lane, per direction (transmit and receive). When
using 8B/10B encoding, this supports a data rate of 2.0 Gb/s per lane.
The XA Spartan-6 LXT devices include one integrated Endpoint block for PCI Express technology that is compliant with the
PCI Express Base Specification Revision 1.1. This block is highly configurable to system design requirements and operates
as a compliant single lane Endpoint. The integrated Endpoint block interfaces to the GTP transceivers for serialization/de-
serialization, and to block RAMs for data buffering. Combined, these elements implement the physical layer, data link layer,
and transaction layer of the protocol.
DS170 (v1.0) March 2, 2010
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