Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
203
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
Consult the Constraints Guide for more information.
For DDR3 SDRAM interfaces that have the memory system input clock
(
sys_clk_p
/
sys_clk_n
) placed on CCIO pins within one of the memory banks, the MIG
tool assigns the DIFF_SSTL15 I/O standard (VCCO = 1.5V) to the CCIO pins. Because the
same differential input receiver is used for both DIFF_SSTL15 and LVDS inputs, an LVDS
clock source can be connected directly to the DIFF_SSTL15 CCIO pins. For more details on
usage and required circuitry for LVDS and LVDS_25 I/O Standards, see the
7 Series FPGAs
SelectIO™ Resources User Guide
(UG471)
.
I/O Standards
These rules apply to the I/O standard selection for DDR3 SDRAMs:
• Designs generated by the MIG tool use the SSTL15_T_DCI and DIFF_SSTL15_T_DCI
standards for all bidirectional I/O (DQ, DQS) in the High-Performance banks. In the
High-Range banks, the tool uses the SSTL15 and DIFF_SSTL15 standard with the
internal termination (IN_TERM) attribute chosen in the GUI.
• The SSTL15 and DIFF_SSTL15 standards are used for unidirectional outputs, such as
control/address, and forward memory clocks.
• LVCMOS15 is used for the
RESET_N
signal driven to the DDR3 memory.
The MIG tool creates the XDC using the appropriate standard based on input from the GUI.
DDR2 SDRAM
This section describes guidelines for DDR2 SDRAM designs, including bank selection, pin
allocation, pin assignments, termination, I/O standards, and trace lengths.
Design Rules
Memory types, memory parts, and data widths are restricted based on the selected FPGA,
FPGA speed grade, and the design frequency. The final frequency ranges are subject to
characterization results.
Pin Assignments
The MIG tool generates pin assignments for a memory interface based on physical layer
rules.
Bank and Pin Selection Guides for DDR2 Designs
Xilinx 7 series FPGAs are designed for very high-performance memory interfaces, and
certain rules must be followed to use the DDR2 SDRAM physical layer. Xilinx 7 series FPGAs
have dedicated logic for each
DQS
byte group. Four
DQS
byte groups are available in each
50-pin bank. Each byte group consists of a clock-capable I/O pair for the
DQS
and 10