Memory Mapping of 8085
Memory interfacing is used to provide more memory space to accommodate complex programs for more complicated systems. Types of memories which are most commonly used to interface with 8085 are RAM, ROM, and EEPROM. 8085 can access 64kB of external memory. It can be explained as- total number of address lines in 8085 are 16, therefore it can access 2^16 = 65535 locations i.e. 64kB.
Note: 2^n=number of memory locations. Where, n = number of address linesSome of the RAM IC's are given as:
1. IC 2114 -> 1k x 4bits
2. IC 6116 -> 2k x 8bits
3. IC 6264 -> 8k x 8bits
Some of the ROM IC's are given as:
1. IC 2708 -> 1k x 8bits
2. IC 2716 -> 2k x 8bits
3. IC 2732 -> 4k x 8bits
4. IC 2764 -> 8k x 8bits
5. IC 27128 -> 16k x 8bits
6. IC 27256 -> 32k x 8bits
7. IC 2708 -> 64k x 8bits
Q. Design a minimum system to interface the following specification:
1. 32kB of RAM using 2 x 16kB RAM IC
2. 32kB of ROM using 2 x 16kB ROM IC
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RAM IC- 3 |
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Interfacing Memories with 8085
Memories can be interfaced in two ways:1. Partial decoding: In this type of decoding not all the address lines are utilized in the circuit (they are left as unused pins). Ex: In an interface of 4kB memory only A0-A11 address lines are utilized, whereas the remaining A12-A15 address lines are unused.
2. Complete decoding (exhaustive decoding): In this type of decoding, all the address lines are utilized in circuit for some or the other use (i.e. all pins are exhausted). Ex: In an interface of 4kB memory only A0-A11 address lines are utilized, whereas the remaining A12-A15 address lines are used in Memory selection logic or as any other control signals.
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