This would be the tightest possible form of encoding
that preserves all allowable combinations of control signals. In practice, this
form of encoding is not used, for two reasons:
• It is as difficult to program as a pure decoded (Wilkes) scheme. This point is
discussed further presently.
• It requires a complex and therefore slow control logic module.
Instead, some compromises are made.These are of two kinds:
• More bits than are strictly necessary are used to encode the possible combinations.
• Some combinations that are physically allowable are not possible to encode