You could also try to interface a PCMCIA card to your microcontroller. The interface to a PCMCIA card is almost identical to that of an IDE connector or a Compact Flash card.

I suggest this because there are available PCMCIA cards that have SRAM storage as opposed to FLASH. They may be more limited in total capacity than flash but may suit your needs. It is possible to interface a PCMCIA card as pages of random access memory in page sizes of 2K bytes (or 4K if I recall). For this type of interface you must provide some 11 or 12 bits of memory addressing to the card and use the memory access control signals on the 68-pin connector as opposed to the I/O control mode signals. Do note that you would still have to support also communications to the internal registers of the card via the I/O signals to support the block level access into and out of the card. The RAM access I discuss above is simply a random acess way to read/write the block buffer inside the PCMCIA card without having to keep a block buffer inside the microcontroller memory space.

This link sheds some light on the use of PCMCIA SRAM cards.

http://www.triangledigital.com/man2020f/ch7ram.htm

Finally note that some PCMCIA flash cards and compact flash cards also support a block memory interface access mechanism to the cards block buffer for random access into the block memory buffer. This is often not used in microcontroller applications because of the additional 18 to 20 interface lines required.

If I were looking seriously at a 512 MByte data store memory I would consider carefully if SRAM or DRAM were a suitable method to use. It takes a lot of time for an 8051 type microcontroller to accumulate that amount of data and this implies that power backup may be an essential part of a robust solution. As such a CF card solution is an easy way to achieve non-volatile storage without having to mess around with batteries of backup power sources.

Michael Karas