Bits within the I/O status register (IOSR). These bits are used to track a change from a previous known or unknown signal value at the corresponding I/O pin (IO0–IO3) when the asynchronous serial port is enabled (that is, when the reset asynchronous serial port (URST) bit of the asynchronous serial port control register (ASPCR) is 1). For example, DIO0 indicates a change on the IO0 pin. See also CIO0–CIO3 bits; IO0–IO3 bits.