The USARTcan also work in a Syncrounous mode , you send a clock along with the data ) They can usually work quite a bit faster than the 115Kbd of normal Uarts , You normally see USARTS built into Micro Processors more than stand allone , but there is a couple of stand allone devices around
Thank you very much, GhostA.
But in MCS51 family that has only UART, it can set for synchronous mode.
So UART and USART can use both synchronous and asynchronous mode.
Does it mean UART and USART has no differeces except USART can use faster than 115k a little? Thank you. :wink:
Thank you very much, GhostA.
But in MCS51 family that has only UART, it can set for synchronous mode.
So UART and USART can use both synchronous and asynchronous mode.
Does it mean UART and USART has no differeces except USART can use faster than 115k a little? Thank you. Wink
It is wrong that UART and USART has no differeces except USART can use faster than 115k.
In synchronous mode the device require both data and clock. The clock is recovered from the data or an external one which is in synchrounous with data.
In asynchronous mode the device requires only data. The data clock is internally generated and synchronised with start and stop bits embedded in the data received.
In synchronous case the data is continuous at fixed rate.
In asynhronous case the data need not be continuous or may be burst data but transmitted at fixed rate.
A UART or Universal Asynchronous Receiver-Transmitter is a piece of computer hardware that translates between parallel bits of data and serial bits. A UART is usually an integrated circuit used for serial communications over a computer or peripheral device serial port. UARTs are now built into some microcontrollers (for example, PIC16F628). USART refers to UART with synchronous implementation.
The word "asynchronous" indicates that UARTs recover character timing information from the data stream, using designated "start" and "stop" bits to indicate the framing of each character. In synchronous transmission, the clock data is recovered separately from the data stream and no start/stop bits are used. This improves the efficiency of transmission on suitable channels; more of the bits sent are data. An asynchronous transmission sends nothing over the interconnection when the transmitting device has nothing to send; but a synchronous interface must send "pad" characters to maintain synchronism between the receiver and transmitter. The usual filler is the ASCII "SYN" character. This may be done automatically by the transmitting device.
Some chips have both synchronous and asynchronous modes. These are called USARTs (for "universal synchronous asynchronous receiver-transmitters")