20. Decoder

The demultiplexer circuit can be transformed into a decoder.

The decoder determines type of the input bit pattern, therefore it is a circuit useful to interpret bit patterns.

Address inputs A and B specify a binary number.

The output matches the specified binary address input as follows:

• only one single output is set to 1, while the rest of the outputs are 0s.

An example of a bit pattern would be an OPCODE that specifies the type of the CPU instruction.

If the number of addressing inputs (A, B, ...) is equal to k, then the number of output lines becomes 2^k.