EXAMPLES OF MEMORY INTERFACING-Free 8085 Microprocessor ARTICLES

EXAMPLE-2

Consider a system in which the available 64kb memory space is equally divided between EPROM and RAM. Interface the EPROM and RAM with 8085 processor.

Implement 32kb memory capacity of EPROM using single IC 27256.
32kb RAM capacity is implemented using single IC 62256.
The 32kb memory requires 15 address lines and so the address lines A0 - A14 of the processor are connected to 15 address pins of both EPROM and RAM.
The unused address line A15 is used as to chip select. If A15 is 1, it select RAM and If A15 is 0, it select EPROM.
Inverter is used for selecting the memory.
The memory used is both Ram and EPROM, so the low RD and WR pins of processor are connected to low WE and OE pins of memory respectively.
The address range of EPROM will be 0000H to 7FFFH and that of RAM will be 8000H to FFFFH.

EXAMPLE-1

Consider a system in which the full memory space 64kb is utilized for EPROM memory. Interface the EPROM with 8085 processor.

The memory capacity is 64 Kbytes. i.e
2^n = 64 x 1000 bytes where n = address lines.
So, n = 16.
In this system the entire 16 address lines of the processor are connected to address input pins of memory IC in order to address the internal locations of memory.
The chip select (CS) pin of EPROM is permanently tied to logic low (i.e., tied to ground).
Since the processor is connected to EPROM, the active low RD pin is connected to active low output enable pin of EPROM.
The range of address for EPROM is 0000H to FFFFH.