The designer must be familiar with the specification and the basic electrical operation of the LPDDR/DDR2 interface. Data bus, data strobe, and data mask (byte enable) signals are point-to-point, whereas all other address, control, and clock signals are not point-to-point. The following figures show the connectivity of the SmartFusion2/IGLOO2 LPDDR interface and a 32-bit DDR2 interface respectively.
For a 4-bit or 8-bit DRAM, all DQ pins are interchangeable. All 4-bit and 8-bit DQ pins are interchangeable in LPDDR, DDR2, and DDR3 memories. For a 16-bit DRAM, DQ0 through DQ7 are interchangeable. Also, DQ8 through DQ15 are interchangeable. However, DQ0-7 pins or signals must not be interchanged with the DQ8-15 pins or signals.
Short ECC_TMATCH_ OUT and ECC_TMATCH_ IN when using ECC bits.
With short traces, the address, control, and command signals might not require both parallel (RT) and series (RS) termination. In a worst-case scenario, a small series resistor (RS) of about 10 Ω or less is required. This series termination is not used for impedance matching, but for dampening the signals.