AR# 41752: MIG 7 Series DDR3/DDR2 - Can a x16 interface fit into a single bank?
MIG 7 Series DDR3/DDR2 - Can a x16 interface fit into a single bank?
Is it possible to fit a x16 DDR3/DDR2 interface into a single bank when generating the interface through MIG?
It is possible to fit a x16 interface in a single bank. However, the feasibility of a single bank x16 solution depends on the density of the x16 component (i.e., number of address pins), implementation of available pin reductions options (noted below), and possibly the target data rate. The following implementation options should be considered to reduce the interface pin-count and determine if the x16 interface can be placed in a single bank:
Use Internal Vref which allows the Vref pins to be used as normal I/O pins freeing up two pins per bank where inputs are utilized. Note: Internal Vref is only an option for data rates below 800 Mb/s. For details, see (Xilinx Answer 42036).
Disable CS_N in single rank configurations. Chip Select only needs to be driven from the FPGA in multi-rank configurations. Single-rank configurations always have CS_N enabled, so the pin on the memory component can be tied Low (active low signal).
Starting with MIG 1.2 (released with ISE 13.2 software), the Memory Options screen includes a Controller Chip Select Pin option. Selecting Disable removes the CS_N pin from the interface freeing up one I/O pin.
Disable Data Mask (DM) - Data Mask can be disabled through the 7 Series MIG tool for designs not requiring the ability to mask data. This saves one I/O pin per DQS byte group (two I/O pins for an x16 interface).
Use DCI Cascade to free up two I/O pins (VRN/VRP). Note that the VRN/VRP pins are not within the T* byte groups. Data group signals CANNOT be placed on VRN/VRP. RESET _N can ALWAYS be placed on an available VRN/VRP signal. The remaining Address/Control signals are ONLY allowed on VRN/VRP when ALL of the following conditions are met. Please refer to the Design Guidelines section of the 7 Series FPGAs Memory Interface Solutions User Guide (UG586) for full details.
DCI cascade is used.
The adjacent byte group (T0/T3) is used as an address/control byte group.
An unused pin exists in the adjacent byte group (T0/T3) or the CK output is contained in the adjacent byte group.
VRN and VRP signals (or the non-byte group signals in, for example, HR column banks) are the top and bottom signals within a bank. To utilize both VRN and VRP for address/control, place the Address/Control byte groups on T0 and T3 within the bank.This places one address/control byte group adjacent to VRN and the other adjacent to VRP.
Move the RESET signal to another bank. This might require the use of a level shifter depending on the Vcco of the chosen bank. This pin can be in any bank because it is an asynchronous signal to the memory. If reset_n is moved to another bank, users must ensure timing is met to ensure correct functionality.
Drive the input sys_clk pair from a different bank within the same I/O column. For full Clocking Guidelines, see (Xilinx Answer 40603).