PROFIBUS Manual

UART coding

UART coding

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UART coding

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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