【正文】 nd function of data between the ponents of the ability to send errorfree. Flow control and hang in some conditions, the data phase handshake signals are replaced, resulting in two with no data transfer phase of the transaction. When the host is ready to receive a batch of data when it sends the input tag. Feature port through the return packet, or if unable to return data, NAK, or STALL handshake is returned as a response. NAK means the feature is temporarily unable to return data, and STALL be stopped permanently, said the port needs to USB system software intervention. If the host receives a legitimate data packets, then it uses ACK handshake to answer. If you receive data with the host detects an error, then it does not return handshake contracted out features. Control of transmission at least two transaction stages: the establishment and status. Transmission can be selectively controlled, including the establishment and status data between the stages of phase. In the establishment phase, the establishment of services for the features of the control port to transmit information. Establishment of issues in the format similar to the output, but the use of the building rather than the output of the PID. Building is always in the establishment of services relative to the use of data DATA0 PID. 10 Before the establishment of the functional ponents must accept the establishment of data and use ACK response, if the data is damaged, then discards the data and do not return to shake hands. Control the data transmission phase, if any, by more than one input or output transaction structure, pliance and batch send the same protocol rules. All the data phase of the transaction must have the same direction (that is, all input or all output). In the data phase, the amount of data to be sent, and its direction is specified in the establishment phase. If the amount of data exceeds the previously identified data packet size, the data in support of the largest packet size of the number of transactions to be sent (input or output). Any remaining data as a residual in the final transaction is sent. Control of the state of transmission phase is the last one operation sequence. State phase at a relatively earlier stage of the data to characterize the changes in flow direction, and always use the DATA1 PID. For example, if the data phase transaction constituted by the output, the state is a single input transaction. If the control sequence is no data transmission phase, then it is by the establishment phase and the subsequent transaction by the input stages, consisting of the state. Interrupt transactions may consist of IN or OUT transfers. Upon receipt of an IN token, a function may return data, NAK, or STALL. If the endpoint has no new interrupt information to return (., no interrupt is pending), the function returns a NAK handshake during the data phase. If the Halt feature is set for the interrupt endpoint, the function will return a STALL handshake. If an interrupt is pending, the function returns the interrupt information as a data packet. The host, in response to receipt of the data packet, issues either an ACK handshake if data was received errorfree or returns no handshake if the data packet was received corrupted. Such endpoints use multiple transactions in a microframe as defined in that section. Each transaction for a highbandwidth. When an endpoint is using the interrupt transfer mechanism for actual interrupt data, the data toggle protocol must be followed. This allows the function to know that the data has been received by the host and the event condition may be cleared. This “guaranteed” delivery of events allows the function to only send the interrupt information until it has been received by the host rather than having to send the interrupt data every time the function is polled and until the USB System Software clears the interrupt condition. 3 Data Toggle Synchronization and Retry The USB provides a mechanism to guarantee data sequence synchronization between data transmitter and receiver across multiple transactions. This mechanism provides a 11 means of guaranteeing that the handshake phase of a transaction was interpreted correctly by both the transmitter and receiver. Synchronization is achieved via use of the DATA0 and DATA1 PIDs and separate data toggle sequence bits for the data transmitter and receiver. Only in the receiver can receive data and with the correct data PID received errorfree packet when the receiver sequence bit before switching. But only in the data transmitter to receive a legitimate ACK handshake when the transmitter sequence bit before switching. Data transmitter and receiver must be synchronized in the transaction the beginning of the timing of their position. Synchronization mechanism used varies with the transaction type. ISO does not support data transmission switch synchronization. Control transfers use the SETUP token for initializing host and function sequence bits. Figure 844 shows the host issuing a SETUP packet to a function followed by an OUT transaction. The numbers in the circles represent the transmitter and receiver sequence bits. The function must accept the data and return ACK. When the function accepts the transaction, it must set its sequence bit so that both the host?s and function?s sequence bits are equal to one at the end of the SETUP transaction. If data cannot be accepted or the received data packet is corrupted, the receiver will issue a NAK or STALL handshake, or timeout, depending on the circumstances, and the receiver will not toggle its sequence bit. Any nonACK handshake or timeout will generate similar retry behavior. The transmitter, having not received an ACK handshake, will not toggle its sequence bit. As a result, a failed dat