Technical data

Table Of Contents
S7 Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
21-9
21.4 Uncoordinated Sending of Data with SFB 8/FB 8
"USEND"
Description
SFB/FB 8 "USEND" sends data to a remote partner SFB/FB of the type "URCV".
The send process is carried out without coordination with the SFB/FB partner. This
means that the data transfer is carried out without acknowledgement by the partner
SFB/FB.
S7-300: The data is sent on a rising edge at REQ. The parameters R_ID, ID and
SD_1 are transferred on each rising edge at REQ. After a job has been completed,
you can assign new values to the R_ID, ID and SD_1 parameters.
S7-400: The data is sent on a rising edge at control input REQ. The data to be sent
is referenced by the parameters SD_1 to SD_4 but not all four send parameters
need to be used.
You must, however, make sure that the areas defined by the parameters SD_1 to
SD_4/SD_1 and RD_1 to RD_4/RD_1 (at the corresponding partner SFB/FB
"URCV") agree in:
Number
Length and
Data type.
The parameter R_ID must be identical at both SFBs.
Successful completion of the transmission is indicated by the status parameter
DONE having the logical value 1.
Parameter Declaration Data Type Memory Area Description
REQ INPUT BOOL I, Q, M, D, L, Control parameter request, activates the
data exchange at a rising edge
ID INPUT WORD M, D, constant Addressing parameter ID, refer to
Common Parameters of the
Communication SFCs
R_ID INPUT DWORD I, Q, M, D, L,
constant
Addressing parameter R_ID, refer to
Common Parameters of the
Communication SFCs
DONE OUTPUT BOOL I, Q, M, D, L DONE status parameter:
0: Job not started or still running
1: Job has been executed error-free