Patent GB-1373828-A (GB)
Title: Data processing systems
IPC: G06F13/12
Filed: 1972-01-10
Abstract: 1373828 Data processing HONEYWELL INFORMATION SYSTEMS Inc 10 Jan 1972 [21 Jan 1971] 1117/72 Heading G4A In a data processing system having a store unit (12, Fig. 1, not shown) holding instructions to control the processing of data by a central processor (10), an input/output multiplexer (16) is connected between the store and at least one communicating device (18) and includes an arithmetic unit for pre-processing data under the control of a discrete instruction generator in each device (18). As described a plurality of devices 18 communicates with the store and central processor. A device requesting and being granted service derives a signal (TSPS, Fig. 2, not shown) which is applied to a NAND gate (68) in the three next lower order priority devices to prevent them gaining access. A signal (BGA1) from the multiplexer inhibits all devices. The derived signal (BSPS) results in the generation of a signal to notify the multiplexer that the corresponding device is ready to transmit, receive or alter data. The system involving one of the devices 18 is shown in detail in Figs. 3a-3f. Data is transmitted from the multiplexer to the device 18 on bus 222 and is directed by a switch 27 either to a buffer 34 for a user device 30 or in the case of a command signal to the instruction generator 26. Data is transmitted from a register 32 and from the instruction generator on buses 205, 206 to the arithmetic unit 80 or to control register 75. A timer 70 controls the operation of the multiplexer and supplies signals to a timing unit 35 in each of the devices to indicate when a device is activated and which buses are to be used. If for example a command from an address in store specified by the central processor is accessed by the multiplexer 16 this command is loaded into register 90 in the multiplexer, all the devices being inhibited from gaining access by the generation of the signal BGA1. The address of the device to be accessed is then fed from register 102 to register 75 together with control signals from instruction decode logic 108. Store address signals from register 104 are transferred via switch 82 to system controller 14. Two 18 bit words representing the command are consequently fed sequentially from store and directed to the selected device. A service request from the device 18 is fed to the timing unit 70. After a delay sufficient to allow the priority network to settle the timing unit 35 of the highest priority device seeking access is set to its active state. It may then feed an instruction word on bus 207 to register 75 where it is decoded to generate control signals so that an address signal on bus 205 passes to adder 87 in the arithmetic unit 80. The arithmetic unit utilizes an 18 bit parallel adder to alter data under the control of signals from timing unit 70 controlled by the data command part of an instruction word. Addition, subtraction, AND and OR operations may be performed. During store and load cycles data is passed unchanged through the adder. In a comparison cycle, data read from store 12 is fed via register 90 and switch 92 to the adder. To generate indicator signals if for example the result of any operation is zero, negative or has overflowed check logic 88 monitors the adder output. If the instruction word contained an interrupt command which is satisfied logic circuit 89 signals microinstruction control 40 in the instruction generator 26 to generate a new instruction word and address.