| 摘要 |
<p>A videotex system employs a subscriber unit (22) at a remote location such as a user's home. The subscriber unit (22) employs the user's telephone tone dial (26) for transmission to a communications module at a central location and uses the user's television set (24) for display of information received as frequency-shift-keying signals by the user's telephone (20). At the central location, the system employs a transmission memory (16) containing the currently desired display, and a microprocessor circuit (28) reads the contents of the transmission memory (16) to send it by FSK signals to the remote location. The information contained in the transmission memory (16) comes from a host computer, and an antiquity memory (50) having locations corresponding to those of transmission memory (16) has its associated location reset whenever a transmission-memory location is written. That antiquity-memory location is then incremented whenever the information is sent, and the microprocessor (28) at the central location repeatedly sends the contents of the transmission-memory location that has been sent least frequently as indicated by the contents in the antiquity-memory (50). The invention reduces the cost of the necessary subscriber units, making the videotex service more widely acceptable. The use of the antiquity-memory and repeated data transmission reduces the effects of data transmission errors due to random noise.</p> |
