Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
211
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
• The clock input (
sys_clk
) can be input on any CCIO in the column where the memory
interface is located; this includes CCIO in banks that do not contain the memory
interface, but must be in the same column as the memory interface. The PLL must be
located in the bank containing the clock sent to the memory. To route the input clock
to the memory interface PLL, the CMT backbone must be used. With the MIG
implementation, one spare interconnect on the backbone is available that can be used
for this purpose.
°
MIG core versions 1.4 and later allow this input clocking setup and properly drive
the CMT backbone.
°
CLOCK_DEDICATED_ROUTE = BACKBONE constraint is used to implement CMT
backbone, following warning message is expected. It can be ignored safely.
WARNING: [Place 30-172] Sub-optimal placement for a clock-capable IO pin and PLL
pair. The flow will continue as the CLOCK_DEDICATED_ROUTE constraint is set to
BACKBONE.
u_mig_7series_0/c0_u_ddr3_clk_ibuf/diff_input_clk.u_ibufg_sys_clk (IBUFDS.O) is
locked to IOB_X0Y176
u_mig_7series_0/c0_u_ddr3_infrastructure/plle2_i (PLLE2_ADV.CLKIN1) is locked to
PLLE2_ADV_X0Y1
u_mig_7series_0/c1_u_ddr3_infrastructure/plle2_i (PLLE2_ADV.CLKIN1) is locked to
PLLE2_ADV_X0Y5
......
• For DDR3 interfaces that have the memory system input clock (
sys_clk
) 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.
• It is acceptable to have differential inputs such as LVDS and LVDS_25 in I/O banks that
are powered at voltage levels other than the nominal voltages required for the outputs
of those standards (1.8V for LVDS outputs, and 2.5V for LVDS_25 outputs). However,
these criteria must be met:
a. The optional internal differential termination is not used (DIFF_TERM = FALSE, which
is the default value).
Note:
This might require manually changing DIFF_TERM parameter located in the top-level
module or setting this in the UCF or XDC.
b. The differential signals at the input pins meet the VIN requirements in the
Recommended Operating Conditions table of the specific device family data sheet.
c. The differential signals at the input pins meet the VIDIFF (min) requirements in the
corresponding LVDS or LVDS_25 DC specifications tables of the specific device
family data sheet.
One way to accomplish the above criteria is to use an external circuit that both
AC-couples and DC-biases the input signals. The figure shows an example circuit for
providing an AC-coupled and DC-biased circuit for a differential clock input. RDIFF