Pat4875158

United States Patent 11 Ashkin et al, 4,875,158 Oct. 17, 1989 {11] Patent Number: (45) Date of Patent: [54] METHOD FOR REQUESTING SERVICE BY A DEVICE WHICH GENERATES A SERVICE REQUEST SIGNAL SUCCESSIVELY UNTIL IT IS SERVICED [75] Inventors: Peter B, Ashkin, Los Gatos; Michael Clark, Glendale, both of Calif. [73] Assignee: Apple Computer, Inc., Cupertino, Calif. [21] Appl. No.: 132,121 [22] Filed: Dec. 14, 1987 Related U.S. Application Data [62] Division of Ser. No. 765,396, Aug. 14, 1985. [51] Int, CLs... GO6F 13/14; GO6F 13/38 [52] U.S. CL. ... 364/200; 364/222; 364/240.8; 364/241; 364/245; 364/262.3; 364/284.3; 340/825.08; 340/825,52 [58] Field of Search ... 364/200 MS File, 900 MS File; 340/825.06, 825.07, 825.08, 825.5, 825.52 [56] References Cited U.S. PATENT DOCUMENTS 3,221,307 11/1965 3,646,534 2/1972 3,715,725 2/1973 3,836,888 9/1974 3,863,025 1/1975 3,979,723 9/1976 4,063,220 12/1977 4,071,908 1/1978 Brophy et al. .. (List continued on next page.) FOREIGN PATENT DOCUMENTS 0051425 5/1982 European Pat. Off. . 0104542 4/1984 European Pat. Off. . 59-52331 3/1984 Japan . 1308854 4/1978 United Kingdom . 1518565 7/1978 United Kingdom . 2035636 6/1980 United Kingdom . 2070826 5/1984 United Kingdom . 0143160 6/1985 United Kingdom . 2167274 5/1986 United Kingdom . 0207313 1/1987 United Kingdom . OTHER PUBLICATIONS Hill et al, “Dynamic Device Address Assignment Mechanism”, IBM Technical Disclosure Bulletin, vol. 23, No. 8, Jan. 1981, pp. 3564-3565. Search Report, Dated May 21, 1986, for British Patent Application No. 8607632. Primary Examiner—Raulfe B. Zache Assistant Examiner—Thomas C. Lee Attorney, Agent, or Firm—Blakely, Sokoloff, Taylor & Zafman [57] ABSTRACT A method for requesting service by a device coupled to a host computer through a communication medium. The host computer sets a service request bit of the de- vice to a first logical value to allow the device to pro- duce a service request signal if the device requires ser- vicing. The device determines that it requires servicing and the device sets an internal flag bit to a first logical value to indicate that the device requires servicing. The device monitors a command from the host computer to see if the command is addressed to the device. If the command is not addressed to the device and if the ser- vice request bit is set to a first logical value, then the device generates a service request signal on the medium after the command by holding the communication me- dium low for a first period of time. If the command is addressed to the device, if the device determines that the command is not a command that services the device, and if the service request bit is set to the first logical value, then the device generates a service request signal on the medium after the command by holding the me- dium low for the first period of time and performs the command. If the command is addressed to the device, if the device determines that the command is not a com- mand that ser…