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Bus device for use in a computer system having a synchronous bus

  • US 4,763,249 A
  • Filed: 10/29/1986
  • Issued: 08/09/1988
  • Est. Priority Date: 09/22/1983
  • Status: Expired due to Term
First Claim
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1. A method for transmitting stored data to and from a memory device in a data processing system that includes a plurality of bus devices and a common synchronous communications path for conducting signals thereon, the path including a plurality of command lines, a plurality of data/address lines, a NO ARB line precluding access to the data/address lines during the next cycle for purposes of arbitration when asserted, a BUSY line for indicating that a transaction is in progress during the next cycle when asserted, and at least one timing line for carrying timing signals defining timing cycles, the memory device being connected to the communciations path to operate in cycles in accordance with the timing signals on the timing line and including a plurality of storage locations each associated with a separate bus address, the method comprising:

  • a first step of monitoring the BUSY and NO ARB lines to detect a cycle in which the BUSY line is asserted and that immediately follows a cycle in which the BUSY line was unasserted and the NO ARB line was asserted, such cycle being denominated a command/address cycle;

    a second step of monitoring the command and data/address lines during the command/address cycle to detect one of a read and a write command on the command lines and to detect signals on the data/address lines representing a bus address with which a storage location is associated; and

    a third step of exchanging data between the memory device and another device over the data/address lines on the communications path during a data cycle which is the second cycle after the command/address cycle during which a bus address with which a storage location is associated has been detected on the data/address lines, and during which one of the read and write commands has been detected on the command lines.

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