Patent GB-1505535-A (GB)
Title: Microprocessor system
IPC: G06F9/30
Filed: 1975-03-21
Abstract: 1505535 Program interruption MOTOROLA Inc 21 March 1975 [30 Oct 1974] 11948/75 Heading G4A A method of operating a digital system including a memory, a microprocessor executing program instructions stored in the memory, a bidirectional data bus connected to the microprocessor, first and second peripheral units connected to the bidirectional data bus, and an interrupt conductor connected to the microprocessor and to the peripheral units, comprises generating an interrupt request by one of the peripheral units, producing an interrupt request signal on the interrupt conductor representative of the interrupt request in response to the interrupt request, and addressing a fixed location in the memory by the microprocessor in response to the interrupt request signal, the fixed location containing an address of an interrupt routine. The system comprises a microprocessor chip 1C having peripheral units 19C, 20C, 25C and 31C-33C connected thereto via bidirectional data buses and interface adapter chips 10C, 23C and 27C. Each peripheral unit may be an input/output device such as a keyboard, a teletypewriter, a CRT, or a synchronous or asynchronous modem. The microprocessor chip 1C operates in conjunction with a RAM 3C for temporary data storage, a ROM 5C for permanent data storage, and a program timer 7C which, in response to requests from the microprocessor chip, generates timing signals of extended duration. Each interface adapter chip such as 10C includes an input logic circuit 11C, a control logic circuit 13C with a control register 17C for modifying the logic functions of logic circuit 13C as dictated by control words from the microprocessor chip 1C, and an output logic circuit 15C for transmitting signals to the associated peripheral unit(s). A further microprocessor chip may be connected to the system via the bus 2C. All of the chips may be fabricated using MOS techniques. Fig. 3 (not shown) illustrates maskable and non-maskable interrupt request lines to the microprocessor chip from the peripheral units, the maskable interrupt request lines operating on a priority basis to mask any interrupt request of lower priority than the one currently being serviced. The microprocessor chip has a program-controlled reinitialization input which is responsive to a signal from a power failure detector to place the system elements in a "benign" state during such power failure, and to perform the required instructions necessary to reinitialize the system thereafter. The microprocessor chip 1C (whose internal arrangement is given in Fig. 4 (not shown)) operates as a byte-organized processor on the two eight-bit bytes of sixteen-bit words held in buffer registers (1H, 3H). Conventional program counters (4H, 7H), stack pointer register (5H, 8H), index registers (6H, 9H), A and B accumulators (10H, 11H) and an ALU (13H) are provided, together with a condition code register (12H) which may be used to store an interrupt mask bit indicating whether an interrupt request (IRQ) is to be masked. When an interrupt request (IRQ) is received, the microprocessor completes execution of the current macroinstruction; if the interrupt mask bit in register (12H) is not set an interrupt sequence is started. The contents of components (4H-11H) are stored in memory during this interrupt sequence. The microprocessor responds to the interrupt request (IRQ) by setting the interrupt mask bit in register (12H) so that no further interruption may occur during the interrupt sequence, the microprocessor then branching to an interrupt routine in memory. If the interrupt request (IRQ) is non-maskable, the interrupt mask bit in register (12H) has no effect on the starting of the interrupt sequence, the microprocessor always branching to a non- maskable interrupt routine in memory. The electrical connections within each interface adapter chip and within the entire microprocessor system are respectively given in Figs. 5, 6 (not shown).