PROFIBUS Manual

We differentiate between the following telegram formats:

-Telegrams without data field

-Telegram with variable length of 4 to 249 bytes and therefore a payload in the range 1 to 246 bytes

-Telegram with fixed data length of 8 bytes data

-Token telegram

-For short, positive responses a short telegram has been defined.

 

Telegram without data field:

 

Telegram with variable length:

The PDU has a variable length between 1 and 246 bytes.

 

Telegram with fixed data length:

The PDU has a fixed length of 8 bytes.

 

Token telegram:

 

Short confirmation:

 

SC stands for Short Confirmation. SD means Start Delimiter, where these can assume four different values. ED stands for End Delimiter and marks the end of a telegram. The individual control fields have the following coding for UART:

 

 

SC, SD1, SD2, SD3, SD4 and ED have a Hamming distance from each other of 4 (HD=4), i.e. they differ from each other in at least 4 bits. The individual character SC is therefore also a valid telegram with HD=4.

 

For telegrams that just have to be confirmed, SC is a valid response telegram. For telegrams that must be responded to with data, an SC telegram can be used to signal that the data is not currently available.

 

DA = Destination Address

SA = Source Address

LE = Length

LEr = Length repeated

FC = Function Code

 

PDU = Protocol Data Unit (payload data)

The PDU data field is made up of an address part and the actual payload data. The address part contains 0 to maximum 2 address extension bytes in the form of SAPs (Service Access Points). The payload without SAPs comprises a maximum of 246 bytes and 244 bytes with SAPs.