<processor> An instruction set where a field (a bit or group
of bits) of the instruction word is decoded (either by
hard-wired logic or microcode) to generate signals to
control the functional units, as opposed to horizontal
encoding where the instruction word bits are used as the
control signals directly.
With vertical encoding, which combinations of signals and
operations are possible is dictated by the decoding logic; the
instruction field can only select one of these preprogrammed
combinations. This has the advantage that many control
signals can be generated based on only a few instruction word
bits and only valid combinations of control signals can be
generated, e.g. only one source driving a bus at once. An
instruction set may use a mixture of horizontal and vertical
encoding within each instruction.
