EMC/SRAM speed

[lpcware]

Content originally posted in LPCWare by inspire on Sun Aug 09 15:13:37 MST 2015
Hi,

I want to use the LPC4337 with EMC+32 bit asynchronous SRAM but I can't figure out what the maximum frequency of the SRAM has to be for full performance. The LPC runs with 204 MHz. Do I need a SRAM that with the same frequency or what is the optimum frequency/access time of the SRAM?

In special, ISSI produces many SRAMs with a speed of 8 ns. Since 1/(204MHz) = 4.9 ns this value of 8 ns seems to be too big - or is the SRAM frequency for the LPC somewhere below?

Thanks!
inspire

[lpcware]

Content originally posted in LPCWare by inspire on Mon Aug 10 01:30:24 MST 2015
Hi Mike,

this makes sense, now I understand a similar paragraph for the LPC4337! Thanks a lot!

inspire

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Sun Aug 09 23:14:10 MST 2015
Obviously, the selected RAM devices must be suitable for the speed at which they are accessed.

But the speed of the EMC peripheral itself must be considered also.

See the datasheet (not user manual) for the maximum rate supported.

E.g. On the LPC1778/1788, the CPU max is 120 MHz, but the EMC is only 80 MHz.
Given the limited clock divisors permited for the EMC, one can limit the CPU to 80 Mhz or run the CPU at full speed and set the EMC
to 60 MHz (half the CPU speed).

There are probably similar constraints for the 43xx series. I haven't looked.

Cheers, Mike.