4.1 Bit and Byte Swapping

DDR3 and DDR2 memories support bit swapping, a technique the designer can use to interchange data lines with one another, provided that they correspond to the same byte lane (for example, any bits inside the D[0..7] lane). This is very useful when trying to optimize a DDR layout routing.

The following figure shows an example of the bit swapping technique implemented in the board used as example in this application note.

Figure 4-1. DDR3 Bit Swapping

Byte swapping is another technique that can be used on DDR3 and DDR2 memories. It allows the designer to swap the data lanes with one another, also for the purpose of optimizing the layout. Remember to also swap the DQMx and DQSx signals corresponding to the swapped byte lanes, as illustrated below.

Figure 4-2. DDR3 Byte Swapping