topic LPC4078: using 16bit bus width external SDRAM as program memory in LPC Microcontrollers

LPC4078: using 16bit bus width external SDRAM as program memory

otavioborges — Mon, 03 Jul 2017 20:25:11 GMT

Hello,

I'm developing an application using LPC4078FBD208 and an Alliance AS4C4M16SA SDRAM IC as external memory. After bootup I'm going to load the program data from a SD card, write it on the external memory and switch CPU context to execute from the external memory.

As M4 instructions are 32bit, the SDRAM 16bit bus width represent a problem for this scenario? The memory max clock is 144MHz, therefore I'll need two clock cycles (assuming that MCU core clock will be 120MHz) to fetch an entire instruction through EMC, will I have to reduce the CPU core clock to 60MHz to work with this setup?

Thank you.

Re: LPC4078: using 16bit bus width external SDRAM as program memory

jeremyzhou — Wed, 05 Jul 2017 04:09:36 GMT

Hi Otavio Borges ,

Thank you for your interest in NXP Semiconductor products and

for the opportunity to serve you.

-- I don't think so.

Have a great day,

TIC

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Re: LPC4078: using 16bit bus width external SDRAM as program memory

carstengroen — Wed, 05 Jul 2017 07:14:24 GMT

According to the users manual, the max EMC clock (I'm not 100% sure, but I read the "dynamic EMC timing" that Tmin is 12.5 nSec) is 80 MHz. I think you will have to set the EMC clock divider to 2 to get 60 MHz for the EMC if runinng the CPU at 120 MHz?