What do you understand by address decoding in the case of memory interfacing? Explain address decoding using 3 to 8 decoder.

The method use by the system to select the correct location on the correct chip is called addressing decoding. In another way, it is the process of generating a chip select (CS) or enable signals from the address bus for each device in the system. The address bus lines are split into two sections:

·         The N, MSB are used to generate a chip select (CS) signal for different device. 

·         The M, LSB are passed in the device as address to the different memory cells or internal registers.

                                             ADDRESS BUS

N- bits to decoder(MSB)

M- bits to memory (LSB)

Address decoding can be done using 3 to 8 decoder.

·         Assume a microprocessor with 10 address lines that give total of mapping 1 KB memory.

·         Let us consider that we want to implement all its memory space and we use 128*8 memory chips.

·         So we have 8 memory chips with 128 bytes storage, so we need 3 address lines connected with the decoder to generate 8 different chip select signals and select one of the 8 chips.

·         And 7 address lines to select a particular memory word of the selected chip.

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