Method for operating a communication network and communication network

1. A method for operating a communication network comprising a master and a number of subscribers,

wherein a message comprising a data field is transmitted by the master,

wherein a first of the subscribers, on receiving the message,

reads data out of the data field of the message, so that the data field is empty after reading the data out, and

forwards the message with the data field empty to at least one other of the subscribers, after reading the data out, and

wherein a second subscriber of the at least one other subscribers, on receiving the message with the empty data field, writes data into the empty data field.

2. The method as claimed in claim 1 , wherein the message has a number of address fields, one of the address fields indicating the first subscriber which is to read data out of the data field and another of the address fields indicating the second subscriber of the data field which is to write data into the data field.

3. The method as claimed in claim 1 , wherein the message has at least one counter which is incremented on at least one of reading out and writing into the data field.

4. The method as claimed in claim 3 , wherein incrementing is carried out with different increments depending on whether reading out or writing is performed.

5. The method as claimed in claim 1 , wherein the message has two counters, wherein one counter is incremented exclusively on reading out of the data field and the other counter is incremented exclusively on writing into the data field.

6. The method as claimed in claim 1 , wherein during a writing of data into the data field, the data to be written are logically combined with data already present in the data field.

7. A communication network comprising a master and a number of subscribers,

the master and the subscribers being connected to one another via a data line,

the master comprising a transmit interface to the data line by which the master sends a message to the subscribers and a receive interface to the data line by which the master receives the message from the subscribers after passing through the subscribers,

the message comprising a data field wherein a first of the subscribers, on receiving the message,

reads data out of the data field of the message so that the data field is empty after reading the data out, and

forwards the message with the data field empty, after reading the data out, to at least one other of the subscribers, and

wherein a second subscriber of the at least one other subscribers, on receiving the message with the empty data field, writes data into the empty data field of the message.

8. The communication network as claimed in claim 7 , wherein the message has a number of address fields, one of the address fields indicating the first subscriber which is to read data out of the data field and another of the address fields indicating the second subscriber of the data field which is to write data into the data field.

9. The communication network as claimed in claim 7 , wherein the message has at least one counter which is incremented on at least one of reading out and writing into the data field.

10. The communication network as claimed in claim 9 , wherein incrementing is carried out with different increments depending on whether reading out or writing is performed.

11. The communication network as claimed in claim 7 , wherein the message has two counters, wherein one counter is incremented exclusively on reading out of the data field and the other counter is incremented exclusively on writing into the data field.

12. The communication network as claimed in claim 7 , wherein during a writing of data into the data field, the data to be written are logically combined with data already present in the data field.

13. A method for operating a communication network comprising a master and a number of subscribers,

wherein the master transmits a message to the subscribers, the message comprising a data field and at least two address fields associated with the data field and addressing that data field, one address field indicating a first subscriber which is to read data out from the data field and another address field indicating a second subscriber which is to write data into the data field, the second subscriber being located downstream of the first subscriber with respect to a running direction of the message,

wherein the second subscriber, on receiving the message with the data field read out by the first subscriber, writes data into the data field of the message, the data field having a storage space read out by the first subscriber, the entire storage space of the data field being available to the second subscriber for writing data into the data field by the second subscriber.

14. The method as claimed in claim 13 , wherein the message has at least one counter which is incremented on reading out and on writing into the data field, wherein incrementing is carried out with different increments depending on whether reading or writing is performed.

15. The method as claimed in claim 13 , wherein the message has two counters, wherein one counter is incremented exclusively on reading out of the data field and the other counter is incremented exclusively on writing into the data field.

16. The method as claimed in claim 13 , wherein during a writing of data into the data field, the data to be written are logically combined with data already present in the data field.

17. The method as claimed in claim 13 ,

wherein the first subscriber reads data out of the one data field of the message so that the one data field is empty after reading the data out,

wherein the first subscriber, after reading the data out, forwards the message with the one data field empty, and

wherein the message with the empty data field is received by the second subscriber which writes data into the empty data field.