External SDRAM bank selection on LPC407x

[otavioborges]

Hello,

I'm currently developing an application using LPC4078FBD208 that will use 3 external AS4C4M16S SDRAM ICs from Alliance.

I've been following AN10950 to perform connections between SDRAM and MCU. Example from Fig. 5 on the AN is the most similar with my SDRAM IC pinout. But I have a question on the Address Bus.

I noticed that MCU pins EMC_A[0:23] have been connected to memory address bus and the two bank pins to EMC_A13 and EMC_A14.

My doubt exactly is why EMC_A12 was skipped (A11 from SDRAM is connected to EMC_A11 but BA0 was connected to EMC_A13). There's a particular reason from that? This example is for LPC24XX family but is directly applicable to LPC407x family?

[Carlos_Mendoza · Accepted solution]

Hi Otavio,

You must use A13 and A14 instead of A12 and A13. The LPC4088 always uses A13/A14 to output the bank select signals, independent of the SDRAM memory organization. Yes, you can use the application note as reference for your design.

Hope it helps!

Best Regards,
Carlos Mendoza
Technical Support Engineer