Technical data

Table Of Contents
Overview over the S7 Communication and the S7 Basic Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
20-10
A5E00739858-01
Existing connections of communication SFBs for configured S7 connections cannot
be used by the communication SFCs for non-configured S7 connections.
Once you have triggered a job, the connection established for the job can only be
used for this particular job. Other jobs involving the same communication partner
can then only be executed after the current job is completed.
Note
If your program includes several jobs involving the same communication partner,
make sure that you call the SFCs for which W#16#80C0 is entered in RET_VAL
again later at a suitable point in time.
Identifying a Job
If you have triggered a data transfer or a connection abort with one of the
communication SFCs for non-configured S7 connections and you call this SFC
again before the current transfer is completed, the reaction of the SFC depends on
whether the new call involves the same job. The following table explains which
input parameters specify a job for every SFC, If the parameters match those of a
job that is not yet completed, the SFC call counts as a follow-on call.
Block Job is identified by
SFC 65 X_SEND DEST_ID, REQ_ID
SFC 67 X_GET DEST_ID, VAR_ADDR
SFC 68 X_PUT DEST_ID, VAR_ADDR
SFC 69 X_ABORT DEST_ID
SFC 72 I_GET IOID, LADDR, VAR_ADDR
SFC 73 I_PUT IOID, LADDR, VAR_ADDR
SFC 74 I_ABORT IOID, LADDR
Reaction to Interrupts
The communication SFCs for non-configured S7 connections can be interrupted by
higher priority OBs. If the same SFC with the identical job is called again by the
interrupting OB, this second call is aborted and a corresponding entry made in
RET_VAL. The execution of the interrupted SFC is then continued.
Access to the Work Memory of the CPU
Regardless of the number of user data to be transferred, the communication
functions of the operating system access the work memory of the CPU in fields of
the maximum length, so that the interrupt reaction time is not extended by the use
of communication functions.
Depending on how you set the maximum cycle load resulting from communication
with STEP 7, the work memory can be accessed several times during the
execution of a job by the communication functions of the operating system.