Memory Address Decoding

Binary Decoders - Decoders have 2n-inputs and n outputs, each input combination results in a single output line contain a 1, and all other lines contain a 0 on the output. Examples of use are decoding memory addresses and CPU instructions.Typically Decoders have an enable when 1 enables decoding the input to 1 on a single output, when not enabled all outputs are zero. The switching function for an enabled 2-input binary decoder is:

The 2 to 4 decoder representation is:

Memory Address Decoding - Figure indicate a 16K by 1 bit word memory (8 bit words are implemented by selecting 8 bits as a group, for instance). Since 214 is about 16K, a single decoder would require 14 inputs and 214 output

The memory decoder is linked to the CPU by the address bus. Each memory cell is linked to an output and input data bus, a write/read control, and the decoder which enables the memory cell when the suitable address appears. The decoder ensures that just a single memory cell is activated at a time for either output or input.