Browse Prior Art Database

Telephone Video System Attachment

IP.com Disclosure Number: IPCOM000060410D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 64K

Publishing Venue

IBM

Related People

Brown, MK: AUTHOR [+2]

Abstract

This article describes a system for allowing the attachment of a computer using a cycle steal interface to a telephone video system. Existing telephone video systems are designed to connect to telephone lines through a standard modem. However, in order to use this system as a component of a tele-conferencing system requires direct high speed communication to a computer. The attachment system is designed to enable such communications of a telephone video system to a computer via a cycle steal interface. This system consists of two digital logic cards and several connecting cables. The following describes the features incorporated in the present attachment system: 1. SIGNAL LEVEL CONVERSION. Fig. 1 is a block diagram of the attachment system.

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Telephone Video System Attachment

This article describes a system for allowing the attachment of a computer using a cycle steal interface to a telephone video system. Existing telephone video systems are designed to connect to telephone lines through a standard modem. However, in order to use this system as a component of a tele-conferencing system requires direct high speed communication to a computer. The attachment system is designed to enable such communications of a telephone video system to a computer via a cycle steal interface. This system consists of two digital logic cards and several connecting cables. The following describes the features incorporated in the present attachment system: 1. SIGNAL LEVEL CONVERSION. Fig. 1 is a block diagram of the attachment system. In some applications, it may not be desirable to have the telephone video system in close proximity to the computer. In order to service these applications, the control and data signals on the modem interface port are converted to EIA RS-422 signals using the telephone video system interface card 1, as shown in Fig. 1, for transmission over long cables 2. 2. DATA CLOCK GENERATION. Fig. 2 is a block diagram of the attachment card 3. This card generates a data clock signal which is used to synchronize data transfers between the computer and the telephone video system. The data clock is required by the system to enable the transfer of each data element. Since the telephone video system is designed to transfer a larger data block than is practical in this application, each data block is transferred in several smaller data segments. This is accomplished by interrupting the data clock signal during the time the computer is processing the previous data segment. In this way, both the number of the data segments and the size of each segment are controlled by the computer. 3. CONTROL STRING RECOGNITION. Embedded in the data output from the telephone video system are several different types of control strings which must be detected in order to present correct data to the computer. This is done using data comparators in the control string decode circuit (Fig. 2), on the attachment card, which monitor the entire data block read from the system. When the control string indicating the beginning of the data block is received, the data transfer is started. Once the transfer is in progress, the comparators begin testing for the control string which indicates the end of the data block. When this control string is recognized, the data transfer is terminated. 4. SERIAL/PARALLEL, PARALLEL/SERIAL CONVERSION. Data is transferred to and from the telephone video system in serial mode, while data transfers to and from the computer are performed in parallel mode. This requires that data be converted to the appropriate mode for each system. The conversion from one mode to the other is done by the attachment card 3. This function is coordinated with the data clock generator, to insure that...