1651 - LatticeECP3: Can the CLKP/CLKN outputs of the DDR3 memory controller be placed on the top side of the LatticeECP3 device?
The DDR3 (Double Data Rate - 3) CLKP/CLKN pads use a generic output DDR function (ODDR). The recommendation is to place the CLKP/CLKN outputs on the same side that the DQ and DQS pads are located. This is because the top side pads are not for the high-speed DDR function that can safely meet the DDR3 performance requirement on the LatticeECP3 device. Note that DDR3 DQ/DQS pads can be located only on the left or right side. Therefore, it is recommended that you locate the CLKP/CLKN pads on the left or right side depending on where the DQ/DQS pads are located.
See
TN1180 LatticeECP3 High-Speed I/O Interface, DDR3 Pinout Guidelines section for more general pinout guidelines.