User Program Considerations - Siemens SIMATIC S7 System Manual

8.5.1.9

User program considerations

After a DP master successfully configures the EM DP01 PROFIBUS DP module, the
EM DP01 and the DP master enter data exchange mode. In data exchange mode, the
DP master writes output data to the EM DP01, and the EM DP01 then responds with the
most recent S7-200 SMART CPU input data. The EM DP01 continuously updates its inputs
from the S7-200 SMART CPU in order to provide the most recent input data to the
DP master. The EM DP01 then transfers the output data to the S7-200 SMART CPU. The
S7-200 SMART CPU places the output data from the DP master into V memory (the output
buffer) starting at the address that the DP master supplied during initialization. The
S7-200 SMART CPU takes the input data to the DP master from the V memory locations
(the input buffer) immediately following the output data.
The user program in the S7-200 SMART CPU must move the output data from the
DP master from the output buffer to the data areas where the program uses it. Likewise, the
user program must move the input data to the DP master from the various data areas to the
input buffer for transfer to the master.
The S7-200 SMART CPU places the output data from the DP master into V memory
immediately prior to the user program portion of the scan. The S7-200 SMART CPU copies
the input data (to the DP master) from V memory to the EM DP01 for transfer to the
DP master after the user program portion of the scan.
The S7-200 SMART CPU transmits the input data to the DP master on the EM DP01's next
data exchange with the DP master.
Status information
There are 50 bytes of special memory (SM) allocated to each expansion module based upon
its physical position. The module updates the SM locations corresponding to the modules'
relative position to the CPU (with respect to other modules). If it is the first module, it updates
SMB1400 through SMB1449. If it is the second module, it updates SMB1450 through
SMB1499, and so on. Refer to the table below:
Table 8- 3
Intelligent
module in
SMB1400 to
SMB1449
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Special memory bytes SMB1400 to SMB1699
Special memory bytes SMB1400 to SMB1699
Intelligent
module in
slot 0 slot 1
SMB1450 to
SMB1499
Intelligent Intelligent
module in module in
slot 2 slot 3
SMB1500 to SMB1550 to
SMB1549 SMB1599
Communication
8.5 PROFIBUS
Intelligent Intelligent
module in module in
slot 4 slot 5
SMB1600 to SMB1650 to
SMB1649 SMB1699
435