PROFIBUS Manual
UART stands for Universal Asynchronous Receiver Transmitter and is the normal coding procedure for serial interfaces. With UART coding every telegram consists of a number of UART characters. Every bit is defined with a static signal level. UART characters are Start-Stop characters with the following structure:
Start |
Bit 1 |
Bit 2 |
Bit 3 |
Bit 4 |
Bit 5 |
Bit 6 |
Bit 7 |
Bit 8 |
Parity |
Stop |
Start = 0 ; Parity = EVEN ; Stop = 1
With EVEN parity, the number of "1" values in data is rounded up to an even number with the parity. Therefore, in order to transmit 8 bits of data, i.e. one byte, 11 bits will always be sent.
Individual telegrams begin with a SYN interval for a Request telegram and a min TSDR intervall for a Response telegram.
The following rules of transmission apply:
1.The quiescent state on the line corresponds to the logical "1" level.
2.Before each Request telegram, a quiescent time should be maintained of at least 33 bits (SYN).
3.Between the individual characters in a telegram no quiescent times are allowed.
4.The receiver checks per character: start bit, stop bit and parity bit
