Abstract: A first device (1) and a second device (2) can be communicated by an electromagnetic coupling. Data to be transmitted from the first device to the second device is converted into pulse signals of different duty ratios in accordance with the H or L level of the transmission data. Further, the oscillation of an oscillator (15) of the first device is intermittently performed in accordance with the H/L level of the pulse signal. Switching elements (39, 40) are provided for a resonance circuit (30) provided in the second device. When data is transmitted from the second device to the first device, the switching elements are turned on or off in accordance with the data. Thus, the electromagnetic coupling is intermittently performed. The oscillator of the first device at that time intermittently executes the oscillation at a third duty ratio.

Abstract: This invention is directed to a data carrier identification system which is used, for example, in production lines. Different data carrier identification numbers (DCNos.) are assigned to respective different data carriers in an access enable area where data carriers can communicate with a central controller. The different DCNos. allow the controller to correctly access a specific data carrier even if more than one data carrier exists in an access enable area. When a new data carrier enters the access enable area its data carrier identification number is checked by the controller to determine if another data carrier already in the area has the same data carrier identification number and, if so, the controller instructs one or more of the data carriers to change their data carrier identification number so that no two data carriers within the access area have the same data carrier identification number.

Abstract: A data transmission system includes a data carrier which has a memory for storing therein data including an identification code and which is attached to an object and a main apparatus having a microwave oscillator so as to conduct communications with the data carrier by use of a microwave, thereby writing data in or reading data from the memory of the data carrier.The main apparatus transmits a microwave modulated by a command or data and thereafter transmits a nonmodulated carrier for a predetermined period of time. On receiving a command, the data carrier executes a read/write operation on the memory and then generates a response. The data carrier receives the nonmodulated carrier sent from the main apparatus so as to conduct a modulation of quadrature phase-shift keying thereon by use of response data, thereby reflectively transmitting the modulated carrier with a plane of polarization shifted from a plane of polarization of the received wave by 90.degree..

Abstract: An article identifying system comprises an ID device attached to an article to be identified and a write/read control apparatus to write and read data into and from the ID device. The control apparatus has an oscillator. The ID device has a resonance circuit. Data transmission is performed by the electromagnetic coupling of the oscillator and resonance circuit. The FSK modulation/demodulation are used in this data transmission. Preferably data is encoded by bi-phase code, f/2f code, bipolar code, or dicode code. An electric power can be also supplied from the control apparatus to the ID device by the continuous oscillation of the oscillator.

Abstract: An ID system includes a data carrier attached to an article to be identified, and an ID controller capable of communicating with the data carrier. The data carrier is provided with first and second data buffers in addition to a readable/writable memory. Data to be written in the memory is temporarily written in the first data buffer. Old data at a location of the memory in which the aforementioned data is to be written is read out of the memory and temporarily stored in the second data buffer. Thereafter, the data in the first data buffer is written in the memory. In order to check whether the data has been written in the memory correctly, the written data is read out of the memory. In the event that a write error is detected in the checking operation, the old data of memory will have been preserved in the second data buffer, thereby enabling recovery of the old data.