EMC Interface on LPC4350

[lpcware]

Content originally posted in LPCWare by gregd on Tue Jun 19 09:50:53 MST 2012
We are designing a board based on the LPC4350 that uses 32 bit wide NOR FLASH (2 16 bit NOR FLASH EMC_CS0), 32 bit wide SRAM (4 16 bit SRAMS EMC_CS2 and EMC_CS3), and 32 bit SDRAM.  Can all of these parts be directly connected to the EMC interface on the LPC4350 with no issues? 

We do currently have 22 ohm series resistors on all of the EMC lines coming out of the LPC4350 to reduce EMI and ringing.  Are these necessary?

On the Hitex board, they are using output buffers for the address and control lines and bi-directional buffers for the data lines.  These buffers are connected to the SRAM and NOR flash parts only.  The SDRAM is connected directly to the LPC4350 with series resistors on the data lines only.  Are buffers recommended or required?  What is the purpose of them on this board?  Are the series resistors on the SDRAM data lines required for proper operation?

How many inputs can be connected to each address, data, or control line on the LPC4350?

Any recommendations/requirements would be very much appreciated. I can't find anything specific in the user manual, data sheet or app notes.

Thanks,
Greg Dunn

[lpcware]

Content originally posted in LPCWare by PhilYoung on Tue Jun 19 14:23:21 MST 2012
You need to compute this based on your design, the capacitance of the memory device inputs, pcb traces etc, so there is no generic answer.
All I know for certain is that having the buffers in the address bus for the SDRAM is a performance killer, these were fitted on the original eval boards and limited the maximum speed for the sdram, so definitely the SDRAM should be connected directly.
Given the number of devices you are trying to connect though I suspect that not using the buffers would load the signals significantly therefore I would fit them anyway.

You can always build a prototype board and not fit them on one board, thanks to the pinout of the buffers it's an easy task to simply wire the inputs and outputs together even for SM devices so you can then measure the signals to determine if they are needed for production.

regards

Phil.