Basics: On Microcontroller

[V]

I have a basic doubt -

Why some of the micro controller provides facility if 9 bit data transmission instead of 8 bit, where do we use 9 bit?

Why do we use 2 stop bit or 1.5 stop bit instead of 1 stop bit?

WHY???


Thanks and regards,
V

 

[jayavardhan]

for providing the data security when preparing some propritary protocol we use 2stpbits or 1.5 stp bits

 

[wek]

The 9th bit intended to distinguish address (9th bit set) and data (9th bit clear) bytes where multiple processors listen to a stream of data on a single bus (e.g. RS-485-based). A processor with a particular address then can ignore all data on the bus until an address byte with matching address arrives.

The extra stopbits are intended to provide extra time for the receiving processor to process the freshly received byte, before a new byte's startbit resets the receiver's shift register. This was valid in the times when UART receivers did not have double buffers (and, more importantly, this was valid for the teletypes, where the "receiver" was mechanical; time has to be provided for the typing mechanism to be engaged). Nowadays, all receivers have double buffering and the processors are fast enough, so that the 1.5-2 stopbits are really just relics now.

JW