Siemens SIMATIC MV500, Operating Instructions Manual, Page: 181 / 294

Process interfacing via an automation system (PLC, PC)
9.4 Control with FB 79
SIMATIC MV500
Operating Instructions, 03/2021, C79000-G8976-C494-05
181
9.4.3 Sample program for data exchange if code length ≤ 27 bytes
Below, you will find a sample program for data exchange when the code length is a
maximum of 27 bytes.
Note
Compatible S7 controllers
The example program can only run on the following S7 controllers:
•
On a CPU 318 and all S7-400 CPUs.
• On all S7-300 CPUs with MMC
On all other S7-300 and S7-400 CPUs, you must use SFCs 14 and 15 for all access to the two
user data interfaces.
Explanation of the program
The example program has the following properties:
•
Only the pure result string with data ID "B#16#81" is output.
• The I/O controller does not check how many bytes the optical reader has returned but
always reads 27 bytes.
The I/O controller does not monitor anything.
• The start of the "Send" user data interface is at address 4 of the process image input.
The start of the "Receive" user data interface is at address 4 of the process image output.
• To ensure the consistency over the entire area of 32 bytes, there must be no update of the
process image during the program shown here.
• The user data is stored in data block DB17 starting at byte 4.
STL program
Table 9- 42 Structure of the STL program
//Enter data ID (in principle only necessary in the first cycle)
L B#16#81 // Only result string
T AB 8
// Check number of data packet for 1
L EB 5 // No. of the data packet from the optical reader
L 1
<> I // If no. ≠ 1
SPB m001 // ... user data is not available yet
// Import user data from the optical reader
L ED 9 // Read first 4 bytes of user data