Depending on the modes that are supported by the hardware, the name of the communication sub-system will usually include a the next bit of the data.
If the Stop Bit does not appear when it is supposed to, the UART considers the entire word to be garbled and will report a Framing Error to the host processor when the data word is read.
The usual cause of a Framing Error is that the sender and receiver clocks were not running at the same speed, or that the signal was interrupted.
The UART takes bytes of data and transmits the individual bits in a sequential fashion.
At the destination, a second UART re-assembles the bits into complete bytes.
Printers and fixed disk devices are not normally serial devices because most fixed disk interface standards send an entire word of data for each clock or strobe signal by using a separate wire for each bit of the word.
In the PC industry, these are known as Parallel devices.In most computer systems, the UART is connected to circuitry that generates signals that comply with the EIA RS232-C specification.There is also a CCITT standard named V.24 that mirrors the specifications included in RS232-C. This means that there will always be a Mark (1) to Space (0) transition on the line at the start of every word, even when multiple word are transmitted back to back.Asynchronous transmission allows data to be transmitted without the sender having to send a clock signal to the receiver.Instead, the sender and receiver must agree on timing parameters in advance and special bits are added to each word which are used to synchronize the sending and receiving units.Synchronous communication is usually more efficient because only data bits are transmitted between sender and receiver, and synchronous communication can be more costly if extra wiring and circuits are required to share a clock signal between the sender and receiver.