Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1 637
UG586 November 30, 2016
www.xilinx.com
Chapter 4: LPDDR2 SDRAM Memory Interface Solution
overall electrical propagation delay. Different die in the same package might have different
delays for the same package pin. If this is expected, the values should be averaged
appropriately to decrease the maximum possible performance for the target device.
These rules indicate the maximum electrical delays between LPDDR2 SDRAM signals:
• The maximum electrical delay between any DQ or DM and its associated DQS/DQS# must
be ≤ ±15 ps.
• The maximum electrical delay between any address and control signals and the
corresponding CK/CK# must be ≤ ±25 ps, with 15 ps being the optimum target.
• The maximum electrical delay between any DQS/DQS# and CK/CK# must be < ±25 ps.
Clocking
The 7 series FPGA MIG LPDDR2 SDRAM design has two clock inputs, the reference clock and
the system clock. The reference clock drives the IODELAYCTRL components in the design,
while the system clock input is used to create all MIG design clocks that are used to clock
the internal logic, the frequency reference clocks to the phasers, and a synchronization
pulse required for keeping PHY control blocks synchronized in multi-I/O bank
implementations. For more information on clocking architecture, see Clocking Architecture,
page 585.
The MIG tool allows you to input the Memory Clock Period and then lists available Input
Clock Periods that follow the supported clocking guidelines. Based on these two clock
periods selections, the generated MIG core appropriately sets the MMCM parameters. The
MIG tool enables automatic generation of all supported clocking structures. For
information on how to use the MIG tool to set up the desired clocking structure including
input clock placement, input clock frequency, and IDELAYCTRL ref_clk generation, see
Creating 7 Series FPGA LPDDR2 SDRAM Memory Controller Block Design, page 528.
Input Clock Guidelines
IMPORTANT: The input system clock cannot be generated internally.
• MMCM Guidelines
°
CLKFBOUT_MULT_F (M) must be between 1 and 16 inclusive.
°
DIVCLK_DIVIDE (D, Input Divider) can be any value supported by the MMCME2
parameter.
°
CLKOUT_DIVIDE (O, Output Divider) must be 2 for 400 MHz and up operation and 4
for below 400 MHz operation.
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