Technical data

S7 Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
21-3
Send and Receive Parameters
If you do not use all send or receive parameters of an SFB/FB, the first unused
parameter must be a NIL pointer (see /232/) and the parameters used must be
located one after the other and without any gaps.
Note for S7-400
During the first call, the ANY pointer specifies the maximum amount of user data
that can be transferred for the job. That is to say, a communication buffer is
created in the work memory of the CPU to ensure data consistency. This buffer
occupies up to 480 bytes of work memory. We recommend you run the first call in
the warm or cold restart OB if the block is not reloaded with the SFB call when the
CPU is in RUN mode.
At subsequent calls you can send/receive any amount of data, however, no more
than with the first call.
The SFBs BSEND and BRCV are an exception to this rule. With them you can
transmit up to 64 Kbytes per job (see Sending Segmented Data with SFB/FB 12
"BSEND" and Receiving Segmented Data with SFB/FB 13 "BRCV"
With SFBs/FBs for bilateral communication:
• The number of the SD_i and RD_i parameters used must match on the send
and receive side.
• The data types of the SD_i and DR_i parameters that belong together must
match on the send and receive side.
• The amount of data to be sent according to the SD_i parameter must not
exceed the area made available by the corresponding RD_i parameter (not
valid for BSEND/BRCV).
ERROR = 1 and STATUS = 4 indicate that you have violated the above rules.
This maximum user data length depends on whether the remote partner is an
S7-300 or an S7-400.
User Data Size
With the SFBs/FBs, USEND, URCV, GET and PUT, the amount of data to be
transmitted must not exceed a maximum user data length. The maximum user data
size depends on:
• The block type used and
• The communication partner.