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Entry type: FAQ Entry ID: 24518053, Entry date: 02/07/2007
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How should you set up the data structure for a SEND job with the loadable driver Allen Bradley Data Highway and which data structure has a message received with the loadable driver Allen Bradley Data Highway?

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Instructions:
The sample projects Datahi3 (for commissioning the Data Highway Protocol on a CP341) and Datahi4 (for commissioning the Data Highway Protocol on a CP441-2) are misleading and do not match the protocol descriptions in the user manual ("Loadable driver for point-to-point CPs, link between CP and Data Highway DF1" in Entry ID 1218110). The structure of the DBs (DB10 in Datahi3 and DB133 in Datahi4) must be corrected as described in the following.
 

No. Procedure
1

Example:
Datahi3 (send the Allen Bradley Data Highway message)
Function block FB8 "P_SND_RK" of CP341 is called cyclically in FC11. 40 bytes are sent from DB10 as from Offset 0.


( 38 KB )
Fig. 01: Data structure UDT1

Each Data Highway "SEND job" must begin with the UDT structure defined above (6 bytes). You can enter the actual user data as from byte 7 (address 6.0).

The length information agreed in DB 10 in the original example (Datahi3) (1st word: "len") is not used. Each Send message must begin with the UDT structure defined above.

2

Example:
Datahi4 (receive the Allen Bradley Data Highway message)
SFB13 "BRCV" for the CP441-2 is called cyclically in FC13. Up to 400 bytes are received in DB133 as from Offset 0.


( 40 KB )
Fig. 02: Data structure UDT2

Each Data Highway Receive message must begin with the UDT structure defined above (6 bytes). The actual user data starts at byte 7 (address 6.0).

The length information agreed in DB133 in the original example (Datahi4) (1st word: "len") is not used. Each Receive message must begin with the UDT structure defined above.

Note:
If the data is to be transferred in both directions, then the examples Datahi3 and Datahi4 are to be extended.

Refer to the manual "Loadable driver for point-to-point CPs, link between CP and Data Highway DF1" in Entry ID 1218110, sections 4.2 and 4.3 for information on sending and receiving messages via the Data Highway Protocol.

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