We are developing a processor board with the MPC8306. We need to use the DDR2 controller to conect the MPC8306 with a 128MB DDR2 Memory (MT47H128M16 from Micron).
We buy a MPC8306 Evaluation board to start de SW development and to use it as refernce design.
We found that the connection between the MPC8306 and the DDR2 memory has a strange way to connect the data bus of the ddr2.
The data bit 0 in the MPC8306 is conected to DQ0 (Ok).
The data bit 1 in the MPC8306 is conected to DQ6 ??
The data bit 2 in the MPC8306 is conected to DQ2 (Ok).
The data bit 3 in the MPC8306 is conected to DQ4 ??
The data bit 4 in the MPC8306 is conected to DQ3 ??
The data bit 5 in the MPC8306 is conected to DQ1 ??
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The data bit 13 in the MPC8306 is conected to DQ14 ??.
The data bit 14 in the MPC8306 is conected to DQ15 ??.
The data bit 15 in the MPC8306 is conected to DQ13 ??.
My question is : Why has the design this strange conection?
We must do the connection in this way or with a standard conection Data bit 0 -> DQ0, Data bit 1 -> DQ1, Data bit 2 -> DQ2, ... , Data bit 15 -> DQ15.
Thank you for your help.
Manuel Ojea
The MPC8306 DDR controller data bus does not require strict byte lanes order or bit lines order in byte lane. Bits in each byte lane can be swapped. DDR SDRAM does not care if signal on the MDQ[0] is most significant bit. It just keeps written '0' or '1' and returns it on read. So the MPC8306 MDQ[0] can be connected to the any of 8 SDRAM's DQ. The only requirement is that selected SDRAM's DQ must be controlled by the MDM0 and MDQS0 which correspond to MDQ[0-7]. Correspondingly MDQ[8-15] can be connected in arbitrary order to the SDRAM’s DQ pins controlled by the MDM1 and MDQS1.
So board designer can swap bits in byte lane to make trace routing easier.
Thank you for the clarification, it is very useful.
Manuel Ojea
Dear Manuel Ojea,
Thank you for your post, however please consider moving it to the right community place for better visibility.
For details please see general advice https://community.freescale.com/docs/DOC-99909
Thank you for using Freescale Community.
Regards,
Wlodek_D.