FRAME # dẫn dắt bởi chủ hiện tại để chỉ bắt đầu và thời gian của một giao dịch. Truyền dữ liệu tiếp tục trong khi FRAME # là khẳng định. Khi FRAME # là de-khẳng định, giao dịch đang ở trong giai đoạn dữ liệu cuối cùng của nó hoặc đã hoàn thành. (s / t / s) Initiator IRDY # Sẵn sàng cho thấy rằng các chủ xe buýt là có thể hoàn thành giai đoạn dữ liệu hiện tại. | Introducing the PCI Bus C BE 3 0 Bus command and byte enables are multiplexed on the same pins. During the address phase of a transaction C BE 3 0 define a bus command. During each data phase C BE 3 0 are used as byte enables to determine which byte lanes carry valid data. C BE 0 applies to byte 0 lsb and C BE 3 applies to byte 3 msb . t s PAR Even Parity across AD 31 0 and C BE 3 0 . All PCI agents are required to generate parity. t s Interface Control FRAME Driven by the current master to indicate the beginning and duration of a transaction. Data transfer continues while FRAME is asserted. When FRAME is de-asserted the transaction is in its final data phase or has completed. s t s IRDY Initiator Ready indicates that the bus master is able to complete the current data phase. During a write IRDY indicates that valid data is present on AD 31 0 . During a read it indicates that the master is prepared to accept data. s t s TRDY Target Ready indicates that the selected target device is able to complete the current data phase. During a read TRDY indicates that valid data is present on AD 31 0 . During a write it indicates that the target is prepared to accept data. A data phase completes on any clock cycle during which both IRDY and TRDY are asserted. s t s STOP Indicates that the selected target requests the master to terminate the current transaction. s t s LOCK Indicates an atomic operation that may require multiple transactions to complete. s t s IDSEL Initialization Device Select is a chip select used during configuration transactions. in 15 PCI Bus Demystified DEVSEL Device Select indicates that a device has decoded its address as the target of the current transaction. s t s Arbitration REQ Request indicates to the central arbiter that an agent desires to use the bus. Every potential bus master has its own point-to-point REQ signal. t s GNT Grant indicates to an agent that is asserting its REQ signal that access to the bus has been granted. Every potential bus .