Form 1023 Instructions Appendix B: Fill & Download for Free

When the software requires data transfer to occur between itself and the USB, it sends a block of data called an I/O Request Packet (IRP) to the appropriate pipe, and the software is later notified when this request is completed successfully or terminated by error. Other than the presence of an IRP request, the pipe has no interaction with the USB. In the event of an error after three retry attempts, the IRP is cancelled and all further and outstanding IRPs to that pipe are ignored until the software responds to the error signal that is generated by sending an appropriate call to the USB. How exactly this is handled depends upon the type of device and the software.As suggested by the name Universal Serial Bus, data transmission in the bus occurs in a serial form. Bytes of data are broken up and sent along the bus one bit at a time, with the least significant bit first as illustrated:The actual data is sent across the bus in packets. Each packet is a bundle of data along with information concerning the source, destination and length of the data, and also error detection information. Since each endpoint sets, during configuration, a limit to the size of the packet it can handle, an IRP may require several packets to be sent. Each of these packets should be the maximum possible size except for the final packet. The USB host has a built in mechanism so that the software can tell it when to expect full sized packets.In the event that a less than maximum size packet is received earlier than expected, an error is assumed and the pipe is stalled with all IRPs being cancelled until the problem is dealt with by the controlling software. If an endpoint is busy, but no error has occurred, it responds with a special signal labelled NAK (Negative AcKnlowedge), which tells the other end of the pipe to wait a while. How these conditions are handled depends on the type of device and the software.Each packet is made up of a set of components called fields including the following, summarised in figure 4 :An eight bit "SYNC" synchronisation field used by inputs to correct their timing for accepting data. Part of this field is a special symbol used to mark the start of a packet.The 8 bit Packet Identifier (PID) which uses 4 bits to determine the type, and hence format, of the packet data. The remaining 4 bits are a 1's complement of this, acting as check bits. Part of this field determines which of the four groups (token, data, handshake, and special) that the packet belongs to, and also specifies an input, output or setup instruction.An address field which gives the address of the function on the end of the pipe to be usedThe 4 bit endpoint field, giving the appropriate endpoint which sends or receives the packet.A data field consisting of 0-1023 bytesThese fields are put together and used by the various types of packets (summarised in Appendix B) for meaningful communication across the USB. Errors are detected by use of a Cyclic Redundancy Check (CRC) on all fields except the PID, which has its own checking mechanism. CRC is considered almost 100% accurate in error detection.Data is sent in packets : →Software checks if it is valid → data is received .Most people don't know about it.Thanks for A2A~DC

When the software requires data transfer to occur between itself and the USB, it sends a block of data called an I/O Request Packet (IRP) to the appropriate pipe, and the software is later notified when this request is completed successfully or terminated by error. Other than the presence of an IRP request, the pipe has no interaction with the USB. In the event of an error after three retry attempts, the IRP is cancelled and all further and outstanding IRPs to that pipe are ignored until the software responds to the error signal that is generated by sending an appropriate call to the USB. How exactly this is handled depends upon the type of device and the software.As suggested by the name Universal Serial Bus, data transmission in the bus occurs in a serial form. Bytes of data are broken up and sent along the bus one bit at a time, with the least significant bit first.The actual data is sent across the bus in packets. Each packet is a bundle of data along with information concerning the source, destination and length of the data, and also error detection information. Since each endpoint sets, during configuration, a limit to the size of the packet it can handle, an IRP may require several packets to be sent. Each of these packets should be the maximum possible size except for the final packet. The USB host has a built in mechanism so that the software can tell it when to expect full sized packets.In the event that a less than maximum size packet is received earlier than expected, an error is assumed and the pipe is stalled with all IRPs being cancelled until the problem is dealt with by the controlling software. If an endpoint is busy, but no error has occurred, it responds with a special signal labelled NAK (Negative AcKnlowedge), which tells the other end of the pipe to wait a while. How these conditions are handled depends on the type of device and the software.Each packet is made up of a set of components called fields including the following, summarised in figure 4 :An eight bit "SYNC" synchronisation field used by inputs to correct their timing for accepting data. Part of this field is a special symbol used to mark the start of a packet.The 8 bit Packet Identifier (PID) which uses 4 bits to determine the type, and hence format, of the packet data. The remaining 4 bits are a 1's complement of this, acting as check bits. Part of this field determines which of the four groups (token, data, handshake, and special) that the packet belongs to, and also specifies an input, output or setup instruction.An address field which gives the address of the function on the end of the pipe to be usedThe 4 bit endpoint field, giving the appropriate endpoint which sends or receives the packet.A data field consisting of 0-1023 bytesThese fields are put together and used by the various types of packets (summarised in Appendix B) for meaningful communication across the USB. Errors are detected by use of a Cyclic Redundancy Check (CRC) on all fields except the PID, which has its own checking mechanism. CRC is considered almost 100% accurate in error detection.