Hello!!

Lately there seems to have been quite a number of questions regarding large amounts of memory and addressing space. There are now quite a lot of 8052 derivatives designed to access large amounts of memory made by various manufactures, so addressing isn't really a problem.

Actually getting lots of memory to connect to your microcontroller however does seem to pose a few problems. First of all, as far as I know, all 8052 devices are of a static nature (i.e. they can run down to 0Mhz) and are designed to interface to static periphials (SRAM etc..). Now this is fine for most applications that only require a small amount of RAM (no more than 32k say), but considering a 32KByte SRAM is normally packaged in a 28-pin DIL case (or some sort of similar SMT case, which is not that much smaller), think how much space and power would be taken up if you needed to implement only 1MB of RAM!!! (1MB = 32 x 32K).. not only that, think how much that would cost!!!

In most system, when a large amount of storage is needed, DRAM is implemented. It is cheaper, and smaller. But there are two disadvantages, the first is it is slower than SRAM, the second is it is difficult to use. A DRAM's memory cells have to be refreshed every so often otherwise they loose their charge, and forget their state, also, the addressing scheme is multiplexed which makes things very complicated. The refresh cycle has to be built into the memory access cycle of the system so it does not 'get in the way' of the processor, and this would be difficult to do with an 8052 has it makes no provision to do so.

What I want to know is, has anyone ever achieved this? If so, how? and does anyone have any experience using low-cost, high-capacity SIMMS such as EDO-RAM with an 8052 or any other static microcontroller? I understand that it is possible to get DRAM controllers which are designed for this task, but I've never been able to find one.

Matt.