UART
1.introduction to UART?
????????* Universal a Synchronous Receiver Transmitter?
????????* uses only two wires : TX to RX (each direction)
????????* can be simple : half-duplex , or full duplex
????????* data is transmitted as frames
2. UART used :
???????* was one of the earliest serial protocols :
---> Serial(com) ports , RS-232 , modems?
???????* popularity of UART is however decreasing :
---> SPI and I2C between components .
---> Ethernet and USB betwween computers and peripheriques?.??
3.?Forms of UART :
There are actually two forms of UART hardware as follows:
#?The?Synchronous?type of transmitters generates the data clock and sends it to the receiver which works accordingly in a synchronized manner.
?#the?Asynchronous?type of transmitter generates the data clock internally. There is no incoming serial clock signal, so in order to achieve proper communication between the two ends, both of them must be using the same?baud rate, and the same frame structure .
4. UART Frame format :
????* idle state :?
when no data is being transmitted the line is held high this allows easy detection of a damaged line or transmitter .
????* Start bit :
indicate data is coming?
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transition from idle (high) to (low)
????* stop bit :
indicate data is complete
stay / return to idle (high)
????* Data bits :
user data
length : 5 to 9 bits (usually 7 or 8)
data is typically send with the least significant bit (LSB) first??
????* Parity bit :?
used for error detection
the value of the parity bit depends on the type of parity being used :
--> even parity : number of 1's must be even
-->odd parity : number of 1's must be odd
5. UART advantages :
Only uses two wires .
No clock signal is necessary .
Provide error detection by parity bit check .
6. UART limitation:
?The size of the data frame is limited to a maximum of 9 bits .
Doesn't supported multiple slave or multiple master systems .
Limited speed is the bottleneck for the application which required higher data transmission rate .