vertical encoding

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 horizontalencoding 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.

(1995-04-23)