An arrangement for synchronizing one or more input/output devices in teleprinters in the context of a subdivision, necessitated by the use of a five-bit code (CCITT 2) for communications transmission purposes, of the total quantity of characters into letters/figures levels employs a storage device in which the level relationship (letters and figure levels) of the character last transmitted or received is stored. A comparator connected to the storage device compares the level relationship of the stored character with that of a character ready for transmission and in the event of disparity operates, via a logic arrangement, to effect the introduction of a level-related switching symbol.