![]() ![]() ![]() Clearly the less data bits the less information you can send, but the faster it will be. The AtMega hardware supports data bits numbering from 5 to 9. In order to save transmission time (in the olden days, heh) you were allowed to specify different numbers of data bits. To produce the above output on an Uno you could write this code: void setup() Without the stop bit, if a byte ended in a zero, then it would be impossible for the hardware to tell the difference between that and the start bit of the next byte. The purpose of the Stop Bit is to ensure that there definitely is a 1-bit between each byte. Thus, at 9600 baud, after receiving a start bit the receiver waits for 156.25 µs, and then samples every 104.16 µs. If the baud rate is 9600 baud, for example, then the sample rate will be 1/9600 = 0.00010416 seconds (104.16 µs). Once the receiver sees the start bit, it waits for 1.5 times the sample time, and then samples the data bits. To indicate the start of a byte, the Start Bit is always indicated by pulling the line low as shown on the graphic. The "idle" time between bytes is transmitted as continuous "1" bits (effectively, the transmit line is held high continuously). The least significant (low-order) bit is transmitted first, thus in the above graphic you see the bits arriving in the order: 01100010. In ASCII this is 0x46 (in hex) or 0b01000110 (in binary). The graphic above shows the letter 'F' being transmitted. This graphic illustrates a single byte being sent: The transmission is asynchronous which basically means that bytes can be sent at any time, with varying gaps between them. Both sender and receiver must be configured to be using the same rate or the receiver will receive meaningless data (due to the bits not being sampled at the same rate that they were sent). The sampling clock is an agreed-upon sample rate (known as the baud rate). Unlike SPI / USB / I2C serial communications does not have a clock signal. A device could be one or more of the following: Asynchronous serial (usually referred to as serial) communications is used to send bytes from one device to another. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |