When you use UART input in FPGA ...

[rezvania]

Hello everyone
I have a question. When we use UART input (Asynchronous input) in FPGA, we use acknowledge to detect valid data and catch it. but we don't send data_valid signal to receiver. Now what we do to detect valid data in receiver? if the line was idle for long time, how do the receiver will find it?
Thanks for your responces

 

[rezvania]

Does anyone use UART for data input in FPGA?

 

[std_match]

I think you want to know how the UART receiver can tell where a byte begins, coming from the idle state.
The idle state is logic '1'. Each transmitted byte is preceded by a "start bit", which is logic '0'.
So when the receiver sees a logic '0', it knows that the next bit is part of a valid byte.

https://en.wikipedia.org/wiki/Asynchronous_serial_communication

 

[shaiko]

Start and Stop bits are used.
A stop bit is the last bit of the communication frame and also the level at which it remain when idle.
A start bit is the first bit of the communication frame and it's always at the opposite level of the stop bit.

For example:
1. If the line is idle, and idle is defined as logic '1' - the first bit of the next frame will always be logic '0'.
2. After that, an X number of payload bits will be sent.
3. At the end the line will sent a stop bit (logic '1') and remain in that level, until the next frame is sent with its start bit.