System having a receive data register for storing at least nine data

Abstract

An asynchronous serial port having a control register and at least one data register exchanges data with a serial bus. The asynchronous serial port includes an indicator representing whether the data register contains all of the data bits, or whether some of the data may be stored in the control register. When a nine-bit data source (or any data source having more than eight bits of data) is received, the bits need not be divided among multiple registers, but can all be stored in the receive-data register. This is particularly useful during DMA or when the exchange of data has been suspended, for example by an interrupt, while additional frames may be received by the asynchronous serial port. Because frames are stored in a single register when an extended write bit or an extended read bit is set. Further, the receive data register also stores status bits associated with received data. This is especially useful during DMA operations, when status, including parity, frame, or overrun errors can be associated with a particular data item examining the stored DMA data itself.