Some AVR chips like the 90S8515 for example can be extended with external RAM (SRAM) memory.

On these chips Port A serves as a Multiplexed Address (A0 – A7)/Data (D0 – D7) bus.

Port C also serves as the upper Address bits (A8 - A15) output when using external SRAM.

 

The maximum size of XRAM can be 64 Kbytes.

 

Example: The STK200 has a 62256 ram chip (32K x 8 bit).

 

Here is some info from the BASCOM user list :

 

If you do go with the external ram , be careful of the clock speed.

Using a 4 MHz crystal , will require a SRAM with 70 nS access time or less. Also the data latch (74HC573) will have to be from a faster

family such as a 74FHC573 if you go beyond 4 MHz.

 

 

You can also program an extra wait state, to use slower memory.

 

Here you will find a pdf file showing the STK200 schematics:

http://www.avr-forum.com/Stk200_schematic.pdf

 

 

If you use a 32 KB SRAM, then connect the /CS signal to A15 which give to the range of &H0000 to &H7FFF, if you use a 64 KB SRAM, then

tie /CS to GND, so the RAM is selected all the time.