8.7.3.4.2 16-Bit DDR3 Interface

Note that the 16-bit wide interface schematic is practically identical to the 32-bit interface (see Figure 8-58 and Figure 8-59); only the high-word DDR memories are removed and the unused DQS inputs are tied off.

When not using all of part of a DDR interface, the proper method of handling the unused pins is to tie off the ddrx_dqsi pins to ground via a 1k-Ω resistor and to tie off the ddrx_dqsni pins to the corresponding vdds_ddrx supply via a 1k-Ω resistor. This needs to be done for each byte not used. Although these signals have internal pullups and pulldowns, external pullups and pulldowns provide additional protection against external electrical noise causing activity on the signals.

The vdds_ddrx and ddrx_vref0 power supply pins need to be connected to their respective power supplies even if ddrx is not being used. All other DDR interface pins can be left unconnected. Note that the supported modes for use of the DDR EMIF are 32-bits wide, 16-bits wide, or not used.

Figure 8-58 32-Bit, One-Bank DDR3 Interface Schematic Using Two 16-Bit DDR3 Devices

Figure 8-59 32-Bit, One-Bank DDR3 Interface Schematic Using Four 8-Bit DDR3 Devices