HID Usage Tables Document 1.1 - C. Scott Ananian

Universal Serial Bus HID Usage Tables 97The second report defined is an Input report that is generated on the interrupt endpoint each time the statusof the display changes. Each of the possible states that can be identified by the display are identified in theDisplay Status collection. This report can also be read over the control pipe to determine the current status.ReportSize(8), ReportCount(1),Logical Maximum(2),Usage(Display Status),Collection(Logical),Usage(Stat Not Ready),Usage(Stat Ready),Usage(Err Not a loadable character),Input(Data, Array, Absolute, No Null),End Collection(),; 8-bit status fieldA second Feature report is defined for getting or setting the current cursor position.Usage(Cursor Position Report),Collection(Logical),ReportID(2),ReportSize(4), ReportCount(1),Logical Maximum(15),Usage(Column),Feature(Data, Variable, Absolute, No Preferred State), ;ColumnLogical Maximum(1),Usage(Row),Feature(Data, Variable, Absolute, No Preferred State), ;RowEnd Collection(),There are a number of ways that data can be transferred between the host and the display: one byte at a time,multiple bytes, or the whole screen using a 32-byte buffered-byte transfer. The choice may depend onwhether the device is implemented as a low-speed or a high-speed device. In this example, a third Featurereport is defined for writing up to four sequential characters from the display in a single report. Note that theData Read Back usage is not declared in the Report descriptor, which implies that the display character datais write-only.Usage(Character Report),Collection(Logical),ReportID(3),ReportSize(8), ReportCount(4),Logical Maximum(126),Usage(Display Data),Feature(Data, Variable, Absolute, Buffered Bytes),End Collection(),;4-byte data bufferVersion 1.1 April 8, 1999