MPC8265 memory

[mig]

Hello,

  I´m designing a board with a MPC8265, and at this moment I have to define the memory architecture. I have reviewed some reference designs of Freescale and I have seen that in all of them the memory used is a SDRAM. The price is not a problem in my case, so in this way I have two questions:

1.-¿Is better to use an asyncrhronous SRAM instead of an SDRAM? SRAM is faster and simpler to use, ¿is ok? Is more expenxisve, but the price is not a problem in this case; it has to be a secure system, so the price is not important.

2.-In other designs that I know, I have seen taht they use a static RAM for 'program memory' and a NVRAM (FRAM) for 'data memory'. I don´t know in fact whats the purpose of those NVRAM. ¿Whats the purpose for using NVRAM?

Taking into account that this is a secure design for a railway system, I would be very grateful if anyone adviced me choosing the best memory architecture. The program will not be very large, so I think with more or less 512KByte is enough for RAM memory.

Thnaks a lot in advance!!

[abartky · Accepted solution]

mig,

The typical uses for Non-Volatile RAM in embedded systems are for Software to use for things such as:

- Storage of software and/or system configuration parameters needed to keep between system reboots, power cycles, etc.

- Use as a file system

- Use as a boot code area to execute initial code from

- Use to store software (somtimes compressed) code and data for download from slower NVRAM to faster RAM on system bootup.

The advantage of NVRAM, Flash, for code storage etc. memories over ROM is that you can do field upgrades, patches, etc. For rugged systems, storing code in Flash is more reliable than using a disk drive.

As far as what kind of RAM (SDRAM, Static, etc.) to use for your system. If cost is not an object and the performance of the software performance of the reference design meets your need, then it is usually the best place to start as you are not paving new ground for hardware design, you know the chip will work in that HW configuration (chips do have bugs also), and you usually make it easier for the software engineers (such as myself) to run as much of the same software as possible on the reference design and the new design such that debugging your system will go a lot more smoothly.

Hope this helps.

- abartky

[mig]

Thanks a lot, really!!