The modularity of the tower system makes it great for prototyping, but for higher speed interfaces, there might be timing/signal integrity issues from having the TWR-MEM.
For example, if you run the NFC demo from MQX 4.2:
C:\Freescale\Freescale_MQX_4_2\mqx\examples\nandflash\build\iar\nandflash_twrk60f120m, It works well standalone, but with TWR-MEM connected. It failed when trying to read the data from nandflash.
Because the NAND flash is on the TWR-K60F120M board, any time you access the NAND flash through NFC the signal will still travel all the way to the MRAM and reflect back which can distort the signals.
Checking with the NFC driver code, you may find the high driven strength of NFC IOs has already been enabled. Decreasing the NFC module clock by setting SIM_CLKDIV4_NFCDIV to 31, the demo still failed.
How to fix it?
Here we provide a trick/solution for this issue:
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then you may set a slower NFC clock by setting SIM_CLKDIV4_NFCDIV to 12, this value can be larger to make the communication more stable, but please note if you try to design a custom board, there is no reason it shouldn’t work at max frequency with a better layout.