External Memory Interface Handbook Volume 2: Design Guidelines

ID 683385
Date 5/08/2017
Document Table of Contents

1.4.2. Pin-out Rule Exceptions for ×36 Emulated QDR II and QDR II+ SRAM Interfaces in Arria II, Stratix III and Stratix IV Devices

A few packages in the Arria II, Arria V GZ, Stratix III, Stratix IV, and Stratix V device families do not offer any ×32/×36 DQS groups where one read clock or strobe is associated with 32 or 36 read data pins. This limitation exists in the following I/O banks:
  • All I/O banks in U358- and F572-pin packages for all Arria II GX devices
  • All I/O banks in F484-pin packages for all Stratix III devices
  • All I/O banks in F780-pin packages for all Arria II GZ, Stratix III, and Stratix IV devices; top and side I/O banks in F780-pin packages for all Stratix V and Arria V GZ devices
  • All I/O banks in F1152-pin packages for all Arria II GZ, Stratix III, and Stratix IV devices, except EP4SGX290, EP4SGX360, EP4SGX530, EPAGZ300, and EPAGZ350 devices
  • Side I/O banks in F1517- and F1760-pin packages for all Stratix III devices
  • All I/O banks in F1517-pin for EP4SGX180, EP4SGX230, EP4S40G2, EP4S40G5, EP4S100G2, EP4S100G5, and EPAGZ225 devices
  • Side I/O banks in F1517-, F1760-, and F1932-pin packages for all Arria II GZ and Stratix IV devices

This limitation limits support for ×36 QDR II and QDR II+ SRAM devices. To support these memory devices, this following section describes how you can emulate the ×32/×36 DQS groups for these devices.

  • The maximum frequency supported in ×36 QDR II and QDR II+ SRAM interfaces using ×36 emulation is lower than the maximum frequency when using a native ×36 DQS group.
Note: The F484-pin package in Stratix III devices cannot support ×32/×36 DQS group emulation, as it does not support ×16/×18 DQS groups.

To emulate a ×32/×36 DQS group, combine two ×16/×18 DQS groups together. For ×36 QDR II and QDR II+ SRAM interfaces, the 36-bit wide read data bus uses two ×16/×18 groups; the 36-bit wide write data uses another two ×16/×18 groups or four ×8/×9 groups. The CQ and CQn signals from the QDR II and QDR II+ SRAM device traces are then split on the board to connect to two pairs of CQ/CQn pins in the FPGA. You might then need to split the QVLD pins also (if you are connecting them). These connections are the only connections on the board that you need to change for this implementation. There is still only one pair of K and Kn connections on the board from the FPGA to the memory (see the following figure). Use an external termination for the CQ/CQn signals at the FPGA end. You can use the FPGA OCT features on the other QDR II interface signals with ×36 emulation. In addition, there may be extra assignments to be added with ×36 emulation.

Note: Other QDR II and QDR II+ SRAM interface rules also apply for this implementation.

You may also combine four ×9 DQS groups (or two ×9 DQS groups and one ×18 group) on the same side of the device, if not the same I/O bank, to emulate a x36 write data group, if you need to fit the QDR II interface in a particular side of the device that does not have enough ×18 DQS groups available for write data pins. Intel® does not recommend using ×4 groups as the skew may be too large, as you need eight ×4 groups to emulate the ×36 write data bits.

You cannot combine four ×9 groups to create a ×36 read data group as the loading on the CQ pin is too large and hence the signal is degraded too much.

When splitting the CQ and CQn signals, the two trace lengths that go to the FPGA pins must be as short as possible to reduce reflection. These traces must also have the same trace delay from the FPGA pin to the Y or T junction on the board. The total trace delay from the memory device to each pin on the FPGA should match the Q trace delay (I2).

Note: You must match the trace delays. However, matching trace length is only an approximation to matching actual delay.
Figure 9. Board Trace Connection for Emulated x36 QDR II and QDR II+ SRAM Interface

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