Patent GB-1515163-A (GB)
Title: Computer interface system with fault detection
IPC: G06F11/07
Filed: 1975-09-11
Abstract: 1515163 Computer interfaces HONEYWELL INFORMATION SYSTEMS ITALIA SpA 11 Sept 1975 [13 Sept 1974] 37375/75 Heading G4A A central processor is linked by an interface comprising a channel 17 (Fig. 5), including a data bus and signal lines to a peripheral unit, both the central processor and the peripheral having parity generating and parity checking circuits, the peripheral unit also having a logic checking circuit for checking errors in command information, signals CS0, CS1 being exchanged if an error is detected in received information and a further signal being sent if it is a parity error to enable a logic checking and monitoring circuit in the central processor to distinguish between errors which are and are not prejudicial to the operation of the system. The arrangement is such that for simple read/write data any error recognition signals are delayed until after the end of data transfer whereas transfer is suspended when logical or parity errors occur in a control character or service information. The central processor comprises a logical unit (3A, Fig. 1, not shown), an input/output controller (3) and a control unit (3B) connected to a main memory (2) and peripheral units (4-13) via device adaptors (14, 20, 21, 22), channels (15-19) linking device adaptors to ports (15A-19A) of the I/O controller. The control unit includes a read only store (46, Fig. 3, not shown) storing micro-programmes which are decoded to provide micro command signals CT1-CTM). Interface. This comprises a channel, e.g. channel 17 (Fig. 5) and an interface module 23. The channel includes a data bus for transmission in either direction of data of control information, unidirectional data strobe lines DS0, DS1, unidirectional control strobe lines (CS0, CS1), operational lines OP0, OP1 (indicating that the module/CPU and device adaptor (i.e. peripheral control unit) are operational), reset lines RS0, enable lines EN1, EN0 and three event lines, EV1 indicating for example that the device adaptor is ready to transfer data, EV2 indicating for example asynchronous events and EV3 indicating parity errors in control information. Four basic dialogues take place:- (1) write without error of information from the processor to the device adaptor, (2) write with error of data information, (3) read without error from the device adaptor to the processor, and (4) read or write with error on control information. An initial 9-bit control character has 1 bit indicating direction of transfer, 7 bits forming the address of a register in the peripheral sub system and 1 parity bit. The type of dialogue is determined by the order of the signals EN0, EN1, CS0, CS1, DS0, DS1 and possibly, in the case of an error, EV3, the four sequences being given in Figs. 6, 7, 8 and 9 (not shown). The device adaptor includes parity check circuits (303, 306, Fig. 14, not shown) verifying received information, a logic incompatibility decoder (307) (setting a flip-flop FIDI to generate a signal (IDI) which may be used to trigger the signal EV2 and setting in the case of a parity error flip-flop FEV3 to generate the signal EV3) and a parity generating circuit (312) calculating the parity bit for information to be transmitted to the CPU. In module 23 (Fig. 12) a parity check network 216 generates a signal ERD1 in the event of a parity error in the received information and at a micro command TC4 (Fig. 13) sets flip-flop ERCE. This flip-flop may also be set at micro command TC9 by a MM error signal from parity control network (120A, Fig. 4, not shown) checking data read out from the main memory unit. In command sending phases and status reading phases each sequence of operation has to be executed in a predetermined time interval. If this is exceeded a flip-flop ERTO is set. If the device adaptor detects a parity or logical error flip-flop EID1 is set. At peripheral unit de-energization flipflop EOP1 is set. At micro command TC6 flip-flops ERCE, ERTO, EOP1 and FEV provide output signals on leads 237, 238, 239, 246, 248, respectively to a register in the CPU, a common error signal MCK being provided if any one of them is set. The signal MCK generates a fixed read-only memory address pointing to for example a micro programme having a diagnostic function which first checks if the read-only store is operating correctly. If it is, errors external to the read-only store are identified. Processing of error signals. When flip-flop ERCE is set during for example a service information transfer (e.g., status of peripheral), signal DCPR enables AND gate 240A so that the error signal is transmitted on line MCK. If neither the read-only store nor the basic network is at fault the supervisor programme decides on a course of action, e.g. retry. If the error is detected during data transfer the transfer is still effected. Similarly if the parity of data read from memory is incorrect transfer is still effected. A time-out error results in the diagnosis programme being effected. The reason for the setting of flip-flop EID1 (i.e. a parity error or a logic error, e.g. due to a command code not being an allowable code) is determined by examining the state of flip-flop EV3 to see if the signal EV3 was present (indicating a parity error).