Programmable cylinder lock which does not require a special change key

A programmable lock, comprising:

• a stator (1),
• a rotor (9) rotatably inserted in stator (1),
• a keyhole for a key (C), formed in said rotor (9),
• a longitudinal groove (3) formed in said stator (1),
• a set of key followers (16) inserted with longitudinal and transversal mobility in said rotor (9) for cooperating with the teeth of the key (C) inserted in said keyhole, each key follower (16) having an element (18) of sliding coupling and having an associated spring (19),
• a set of locking pins (20) inserted with a longitudinal mobility in said rotor (9), said key followers (16) and locking pins (20) having means for mutual coupling,
• a stop bar (23) suitable for cooperating with said groove (3) of stator (1) in order to allow displacement of said locking pins (20) or to immobilize the same,
• a change bar (27), having elements of sliding coupling (28) engaged with said elements of sliding coupling (18) of the key followers (16), and suitable for co-operating with said groove (3) of stator (1) in order to control the mutual coupling of said key followers (16) and locking pins (20),
• wherein said stop bar (23) blocks said locking pins (20) when the stop bar (23) does not correspond to said groove (3) of stator (1), and the stop bar (23) makes free displacement of the locking pins (20) when the stop bar corresponds to said groove (3) and determines a position of insertion and extraction of the key,
• wherein said key followers (16) are coupled with said locking pins (20) when said change bar (27) does not correspond to said groove (3) of stator (1), and are disengaged when said change bar corresponds to said groove (3) and determines a position of key change,
• wherein the programmable lock further comprises a security device (53-56) intended to prevent a faulty effectuation of a change operation, which security device operates by hindering inward displacement of the change bar (27) when the key (C) for programming the programmable lock is inserted in an incomplete manner.