Patent GB-991062-A (GB)
Title: Duplex operation of peripheral equipment
IPC: G06F15/16
Filed: 1963-08-09
Abstract: 991,062. Digital computers. SPERRY RAND CORPORATION. Aug. 9, 1963 [Aug. 23, 1962], No. 31498/63. Heading G4A. An arrangement for selectively connecting one of a plurality of data processors to a peripheral unit comprises first means for receiving and storing control signals from the data processors and a group of second means individually actuable to specify communication between a particular data processor and the peripheral unit, only one of the individual second means being capable of being actuated at any one time. The arrangement described comprises two computer, A and B, and a common magnetic tape peripheral unit, access to which is controlled by a "duplexer" There may be a plurality of different peripheral units each having an associated "duplexer" (Fig. 1, not shown). The circuit shown in Fig. 2 comprises a 30-stage "C register" for receiving data from and transmitting data to the computers A and B, communication with the tapes being via further registers Z and X which translate between 30-bit computer words and the 8-bit characters required for the tapes. The C register is connected also to a function register to control operations in the tape unit in accordance with a control word in the C register. Error detecting circuits are provided to respond to timing or parity errors &c., and transmit information via the C register to the controlling computer to inform it of malfunctions in the tape unit. The computers control the magnetic tape by means of control words transmitted to the C register in conjunction with an "external function" signal. There are three control words affecting the duplexer:- (1) Request control, having bits 001 in the lowest three orders of the control word. Assuming the request originates in the A computer, a flipflop 3-13, Fig. 3, is set and assuming that neither computer is then in control, an "assign control" flip-flop 3-14 is set to enable subsequent setting of an "A control" flip-flop 3-15. The setting of flip-flop 3-14 sets an "interrupt" flip-flop 4-15, Fig. 4A, and to place a "1" in order 24 of the C register. The subsequent setting of flip-flop 3-15 causes gate #A 4-16, Fig. 4A, to transmit an "interrupt" signal to computer A to interrupt the program thereof so that the word in the C register can be stored in the computer. On receipt of this word, the computer transmits an "input acknowledge" signal to clear flip-flop 4-15, the magnetic tape unit now being ready to receive further external function words indicating "read" "write" or "rewind" for controlling its operation, from computer A. If computer B is in control when computer A requests control, the request is stored in flip-flop 3-13 until computer B releases control by releasing flip-flop 3-20. If simultaneous requests from computers A and B occur, flipflops 3-13 and 3-19 are both set, setting of the flip-flop 3-15 via gate A 3-26, so that the request from the B computer is dealt with first. When the A computer has control of the tape unit, an "external function" signal from the computer sets a "reply" flip-flop 4-21, Fig. 4B, to enable a gate #A 4-25 to gate an external function code word from the computer to the C register. If this function word requires output of a data word from the computer, it causes an ODR flip-flop 4-13, Fig. 4A, to be set thereby generating an "output data request" signal to inform the computer that the tape unit is ready to receive a data word. (2) Release local, having bits 100 in the lowest three orders of the control word. Assuming this control word comes from computer A, it is effective only if computer A is in control of the tape unit but is not executing some external function code word previously sent to it by the computer and in these circumstances, an "idle" flip-flop 4-29, Fig. 4B, being set, a gate A 3-29, Fig. 3, is enabled and subsequently the A control flip-flop 3-15, Fig. 3, is released. (3) Release remote, having bits 010 in the lowest three orders of the control word. Assuming this control word comes from computer A, it is effective only if computer B is in control and immediately causes the B control flip-flop 3-20 to be released. If this control word has been preceded by a request control from computer A, computer A takes over control of the tape unit.