In the computer , Bus communication control mainly solves how to know the beginning and end of transmission , And how to coordinate and cooperate with each other .
There are usually four ways ： Synchronous communication 、 asynchronous communication 、 Semi synchronous communication 、 Separate communication .
In asynchronous communication , There are two ways ： Parallel transmission 、 Serial transmission .
In asynchronous serial communication , There is no synchronous clock , There is no need to transmit synchronous signals in data transmission . To confirm the transmitted character , The agreed character format is ：
1 Starting bits （ Low level ）、5~8 Data bits （ Such as ASCLL Code for 7 position ）、1 Two parity bits （ For error detection ）、1 or 1.5 or 2 Stop bits （ High level ）.
1） The start bit is followed by the lowest bit of the character to be transmitted , The parity bit should be the highest bit of the transmitted character , In fact, it is to put the binary number of characters upside down , The end of the whole character is a high level stop bit .
2） The start and end bits form a frame , The interval between two frames is arbitrary , This part of the interval is called the free bit （ High level ）.
3） The less free bits between two frames , The higher the data transmission rate .
Example ： Drawing shows how to send hexadecimal data by asynchronous serial transmission 95H. The character format is required to be ：1 Bit start bit 、8 Digit bit 、1 Bit parity bit 、1 Stop bit . Let's say that every second 120 Data frames , Try to calculate the baud rate 、 Bit rate .
According to the character format given by the title , A frame contains 1+8+1+1=11 position
So the baud rate is ：（1+8+1+1）*120=1320bps=1320 potter
The bit rate is ：1320*（8/11）=960bps