Prime Computer Inc.

Alexander J Stevenson

David M Lounsbury

Donald C Manson

Gordon A Ross

A controller for use with a magnetic tape drive which has a plurality of buffer memories for temporarily storing data that is passed between the tape drive and a host computer system. Temporary storage of data within the tape controller allows data to be rewritten on the tape if the initial writing is faulty and allows data read from the tape to be reconstructed if the data has been erroneously recorded. Transfer of information into and out of the buffer circuits is controlled by two independent direct memory access circuits--one circuit transfers data between the host computer system and the buffer memories and the other circuit transfer data between the buffer memories and the tape drive. Each of the direct memory access circuits operates independently of the other, however, both circuits are coordinated by a central processing unit which communicates with the direct memory access units by means of an interrupt arrangement. The controller also contains a serial input/output unit which allows the controller to format and decode a data format that allows synchronous decoding of the data which in turn permits 'on the fly' error correction.

Magnetic tape drive controller utilizing dual DMA controllers

A digital logic bus termination module that is to be plugged into a TTL logic backplane bus and in which the module includes a TTL logic circuit chip package having multiple terminals including a reference terminal, input terminal and output terminal. The TTL logic circuit chip package comprises an input diode, preferably a Schottky diode connected to the input terminal thereof and forming a bus termination clamping means. The bus line is connected to the input terminal of the chip package while the bus reference line is coupled to the reference or ground terminal for the circuit chip package. The TTL logic circuit chip package has the output terminal thereof unconnected so that only the diode is in operative association with the bus. One or more resistors may also be used in parallel with the clamping diodes for impedance matching purposes.

Digital logic bus termination using the input clamping Schottky diodes

Controller circuitry for a serially-recording magnetic tape drive which is capable of correcting writing errors by rewriting the portions of the data which have been erroneously recorded. Write circuitry in the controller breaks a conventional data record up into one or more blockettes, each of which is assigned a unique sequential blockette number which is recorded on the tape along with the data. After each blockette has been serially recorded sequentially by blockette number on the tape, it is immediately read to check whether it has been properly recorded on the tape. If the blockette has been recorded improperly, the read process directs the write circuitry to rerecord the blockette information at the tape position then under the write head. The recorded blockettes may be out of sequential order since the rerecorded blockette may be located several blockettes after its initial erroneous writing. The data is placed back in sequential order by the read process. As blockettes are read from the tape, they are placed in a buffer memory in the controller. The read circuitry then transfers the data to the host computer system in the order specified by the blockette number and therefore reconstructs the data even if blockettes have been rewritten out of sequence.

Growing community of inventors

Framingham, MA, United States of America

Alexander J Stevenson