3. External Memory
Interfaces in Stratix II and
Stratix II GX Devices
SII52003-4.5
Stratix® II and Stratix II GX devices support a broad range of external
memory interfaces such as double data rate (DDR) SDRAM, DDR2
SDRAM, RLDRAM II, QDRII SRAM, and single data rate (SDR) SDRAM.
Its dedicated phase-shift circuitry allows the Stratix II or Stratix II GX
device to interface with an external memory at twice the system clock
speed (up to 300 MHz/600 megabits per second (Mbps) with
RLDRAM II). In addition to external memory interfaces, you can also use
the dedicated phase-shift circuitry for other applications that require a
shifted input signal.
Introduction
Typical I/O architectures transmit a single data word on each positive
clock edge and are limited to the associated clock speed. To achieve a
400-Mbps transfer rate, a SDR system requires a 400-MHz clock. Many
new applications have introduced a DDR I/O architecture as an
alternative to SDR architectures. While SDR architectures capture data on
one edge of a clock, the DDR architectures captures data on both the
rising and falling edges of the clock, doubling the throughput for a given
clock frequency and accelerating performance. For example, a 200-MHz
clock can capture a 400-Mbps data stream, enhancing system
performance and simplifying board design.
Most new memory architectures use a DDR I/O interface. Although
Stratix II and Stratix II GX devices also support the mature and well
established SDR external memory, this chapter focuses on DDR memory
standards. These DDR memory standards cover a broad range of
applications for embedded processor systems, image processing, storage,
communications, and networking.
Stratix II devices offer external memory support in every I/O bank. The
side I/O banks support the PLL-based interfaces running at up to
200 MHz, while the top and bottom I/O banks support PLL- and
DLL-based interfaces. Figure 3–1 shows Stratix II device memory
support.
Altera Corporation
January 2008
3–1
ALTERA [ ALTERA CORPORATION ]
