could anyone explain me how does "break" work in USART ? and why is it used ?

[mohi@608]

could anyone explain me how does "break" work in USART ? and why is it used ?

i am working on a usart but not able to figure out the need of break ...and how to identify a break condition

 

[std_match]

Re: could anyone explain me how does "break" work in USART ? and why is it used ?

A break is a long '0', so long that the receiver will see it as a zero byte regardless of the receiver baudrate.
The stop bit will also be a zero, so the break condition is identified by all data bits set to '0' together with a framing error.

One usage is to tell the other end to change baudrate.

 

[mohi@608]

Re: could anyone explain me how does "break" work in USART ? and why is it used ?

can break be used in both sync and async transmission ? as in case of sync padiing is done to mantain the channel ?/

 

[std_match]

Re: could anyone explain me how does "break" work in USART ? and why is it used ?

A "break" is an illegal sequence on an asynchronous data line (framing error),
Since there is no illegal sequence on a synchronous data line, a "break condition" is not possible.

 

[mohi@608]

Re: could anyone explain me how does "break" work in USART ? and why is it used ?

then why do we have a extra indication for break, when we already have a framing error ??

 

[std_match]

Re: could anyone explain me how does "break" work in USART ? and why is it used ?

If the UART receiver has extra logic to check for a "break" (checking for a specified length), it can make a better decision.

Without the extra logic, a "break" will only generate a data byte 0x00 with a framing error. In this situation, you can not be sure that is really is a break. It can also be a normal byte with the wrong baud rate.