International Business Machines Corporation

Hasler Ag Bern

Heinrich Meyr

Urs H Bapst

Heinz J Keller

Hans R Muller

Claude Georges

In a ring communication system comprising selectively connectable data stations, each station has connecting circuitry including a phase-locked loop arrangement (111) which is frozen at its current frequency and phase in response to a signal interruption caused by a station insertion or removal operation. Control logic (113) generates a freeze control signal in dependence of the signal energy status on input lines (75). This control signal activates gates (149, 151) and switches (155, 157) to interrupt change control signals of the phase-locked loop circuitry and to keep an oscillator control voltage at a given value. The control logic also provides an auxiliary data signal during the freeze interval which is applied to the ring to keep stations downstream in synchronism. By this method and arrangement, undesired reactions and excursions of the phase-locked loop circuitry in response to a signal energy outage are prevented, and synchronization can be rapidly regained after station insertion or removal.

Method for connecting or disconnecting selected stations in a ring

A mosaic printer is made secure from unauthorized interception of data by falsifying the needle drive pulse current magnitude and sequence so that electromagnetic leakage radiation cannot be used to determine the alphanumeric data being printed. This falsification is accomplished by a compensation device having compensators energized each print cycle in addition to the printer needle drives in a reciprocal or a pseudorandom manner. The compensators have current consumption characteristics nominally identical to the needle drives and produce substantially identical radiation pulses, making it impossible to correlate the radiated pulse format with the symbol being printed.

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Aachen, Germany

Heinrich Meyr