Description:
For the Data Highway protocol there is no separate module available for processing the protocol stack. A retroloadable protocol driver was developed for the upper performance range in order nevertheless to connect systems that exclusively support this protocol to the SIMATIC S7.
Here, the stacks and protocol mechanisms required for the communication are written in software form which then has to be loaded in the CP and licensed.

Here, the asynchronous link full-duplex (DF1) protocol is used for transferring the data. As communication partner you can use all modules on which you can parameterize the DF1 protocol on the "Asynchronous Link" interface.

Physically, the Data Highway protocol can be used on the following media:

• RS 232
• 20 mA (TTY)
• RS 422 / RS485

Protocol services:
The Data Highway protocol exclusively supports the Send/Receive service. This enables active data transfer between two stations. Data is exchanged here between the applications using send and receive blocks on both sides.

Advantages of the protocol:

• Easy connection to the Allen Bradley system
• Suitable for medium to large volumes of data (<= 1024 / 4096 bytes)
• Acknowledged data transfer

Disadvantages of the protocol:

• Great amount of configuration and programming required
• Protocol is not common in the SIMATIC family

Quantity framework:
 

Parameters	Value range
Data area	Up to 1024 / 4096 bytes per job (S7-300 / S7-400)
Logical interface	Layer 7 of the ISO-OSI reference model
Number of possible connections per CP	1 per interface (point-to-point), up to 32 in multipoint systems

Note:
General information on communication via SIMATIC S7 and a detailed description of the Data Highway protocol are available in Entry ID: 20982954.

Keywords:
Serial connection, Third-party system, Data Highway protocol