Siemens SIMATIC S7-400H, Системное руководство

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Consistent data
9.2 Consistency rules for SFB 14 "GET" or read variable, and SFB 15 "PUT" or write variable
S7-400H
System Manual, 03/2012, A5E00267695-11
113
9.2 Consistency rules for SFB 14 "GET" or read variable, and SFB 15
"PUT" or write variable
SFB 14
The data are received consistently if you observe the following points:
Evaluate the entire, currently used part of the receive area RD_i before you activate a new
request.
SFB 15
When a send operation is initiated (rising edge at REQ), the data to be sent from the send
areas SD_i are copied from the user program. You can write new data to these areas after
the block call command without corrupting the current send data.
Note
Completion of transfer
The send operation is not completed until the status parameter DONE assumes value 1.
9.3 Consistent reading and writing of data from and to DP standard
slaves/IO devices
Reading data consistently from a DP standard slave using SFC 14 "DPRD_DAT"
Using SFC14 "DPRD_DAT" (read consistent data of a DP standard slave), you can
consistently read the data of a DP standard slave of IO device.
The data read is entered into the destination area defined by RECORD if no error occurs
during data transfer.
The destination area must have the same length as the one you have configured for the
selected module with STEP 7.
By calling SFC 14 you can only access the data of one module/DP identifier at the
configured start address.
For information on SFC 14, refer to the corresponding Online Help and to the "System and
Standard Functions" manual.
Note
Evaluate the entire currently used part of the receive area RD_i before you activate a new
job.