The region of the PCB used for DDR3 circuitry must be isolated from other signals. The DDR3 keepout region is defined for this purpose and is shown in Figure 7-51. This region should encompass all DDR3 circuitry and the region size varies with component placement and DDR3 routing. Additional clearances required for the keepout region are shown in Table 7-63. Non-DDR3 signals must not be routed on the same signal layer as DDR3 signals within the DDR3 keepout region. Non-DDR3 signals may be routed in the region provided they are routed on layers separated from DDR3 signal layers by a ground layer. No breaks should be allowed in the reference ground or VDDS_DDR power plane in this region. In addition, the VDDS_DDR power plane should cover the entire keepout region.