Gopal Amlekar wrote:
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Hello,
I would like to know how we can access very large memory such as 8MBytes. Is it possible? My wild guess is to use a free port such as Port 1 in addition to port 0 and port 2 to generate a 24 bit address. The port 1 address will be generated manually i.e. by the program whereas port 0 and 2 address bytes will be generated by the 8051 itself. With 24 bit addressing, 16 Mbytes can be accessed.
But whether this is practical? Anyone has used such scheme and proven? Is there any alternative method or we have to resort to 16 bit processors (having 24 bit addressing capability)?
Also please suggest some memory chips for such large amount? It can be either volatile or non volatile (preferred). But data reads and writes will be very frequent.
Thanks to all in advance............

You actually have several choices for very large memory applications.

1. Code Banking
2. 51MX from Philips
3. XA from Philips
4. E5 from Triscend

There are possibly even more. You need to determine your memory and peripheral needs and decide on the processor that suits your needs the best. Each form has its advantages.

Code Banking is likely to be the least expensive as you can use known designs and low cost derivatives. It is well understood and that makes it easier and cheaper to implement. Understand that objects must be limited toe the bank area so if you are store LARGE memory segments this may be limiting factor.

The 51MX is a realtively new kid on the block. Allowing up to 8MB of code space and 8 MB of data space. This memory space can be accessed in many different ways. With the Raisonance tools you can access the memory as linear address space and define objects of unlimited size depending on the physical memory you have designed into your application and the hardware limitations.

The XA is a 16 bit alternative to the 8051. Depending on the varient you have as much as 16MB of memory available. It has been in production for quite a while and is well understood. Pricing is comparable to medium price 8051 derivatives and tools are reasonably priced. An added benifit is much higher processing speeds allowed by hte 16 bit processor and data paths.

Triscend offers a broader addressing range than most 8051 derivatives and the added flexability of definable peripherals. Many of the advantages of all of each of these choices. Biggest downfall may be price, but of course that is a function of volume.

I hope this helps define your options.

Bryan Whitton