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Altera Corporation
10–25
July 2005
Stratix Device Handbook, Volume 2
Transitioning APEX Designs to Stratix & Stratix GX Devices
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A Default Required fMAX setting does not override the PLL clock
settings. Only individual clock settings override the PLL clock
settings.
Therefore, you can enter different project clock settings corresponding to
new PLL settings and accelerate timing analysis by eliminating a full
compilation cycle.
f
For more information about using Stratix and Stratix GX PLLs, see the
General-Purpose PLLs in Stratix & Stratix GX Devices chapter.
I/O Structure
The Stratix and Stratix GX I/O element (IOE) architecture is similar to the
APEX II architecture, with a total of six registers and a latch in each IOE.
The registers are organized in three sets: two output registers to drive a
single or double-data rate (DDR) output path, two input registers and a
latch to support a single or DDR input path, and two output enable
registers to enhance clock-to-output enable timing or for DDR SDRAM
interfacing. A new synchronous reset signal is available to each of the
three sets of registers for preset or clear, or neither. In addition to the
advanced IOE architecture, the Stratix and Stratix GX IOE features
dedicated circuitry for external RAM interfacing, new I/O standards,
differential on-chip termination, and high-speed differential I/O
standard support.
External RAM Interfacing
The advanced Stratix and Stratix GX IOE architecture includes dedicated
circuitry to interface with external RAM. This circuitry provides
enhanced support for external high-speed memory devices such as DDR
SDRAM and FCRAM. The DDR SDRAM interface uses a bidirectional
signal, DQS, to clock data, DQ, at both the transmitting and receiving
device. Stratix and Stratix GX devices transmit the DQS signal with the DQ
data signals to minimize clock to data skew.
Stratix and Stratix GX devices include groups of programmable DQS and
DQ
pins, in the top and bottom I/O banks of the device. Each group
consists of a DQS pin that supports a fixed number of DQ pins. The number
of DQ pins depends on the DQ bus mode. When using the external RAM
interfacing circuitry, the DQS pin drives a dedicated clock network that
feeds the DQ pins residing in that bank. The Stratix and Stratix GX IOE has
programmable delay chains that can phase shift the DQS signal by 90° or
72° to ensure data is sampled at the appropriate point in time. Therefore,
the Stratix and Stratix GX devices make full use of the IOEs, and remove
the need to build the input data path in the logic array. You can make
these I/O assignments in the Quartus II Assignment Organizer.