Technical data

Overview over the S7 Communication and the S7 Basic Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
20-2 A5E00739858-01
Criteria Communication SFCs for Non-
Configured S7 Connections
Communication SFBs for
Configured S7 Connections
Number of
communication partners
The number of communication partners that
can be reached one after the other is not
restricted by the connection resources
available (see
/70/ ,
/101 /). (The connections can be
established and terminated again while the
program is running.)
The number of simultaneously
obtainable communication
partners is restricted to the
number of connection resources
available. It also depends on the
CPU being used (see
/70 /, /101 /).
Maximum user data
length
A user data length of 76 bytes is
guaranteed.
The maximum transferable user
data length depends on the block
type (USEND / URCV, GET, etc.)
and on the communication partner
(S7-300, S7-400 or M7).
Number of variables
transferred per block call
You can only transfer one variable.
• S7-300: one variable
• S7-400: max. four variables
Classification of the
blocks
The SFCs for the S7 Basic Communication
are system functions. Therefore, they do
not require user memory.
The SFBs/FBs for the S7 Basic
Communication are system
function blocks. Therefore, they
require an instance DB for the
actual parameters and the static
data.
Dynamic modification
of the address
parameters
Dynamic modification of the address
parameters is possible: on completion of
the active job, you can address other
communication partners.
S7-300: You can reconfigure the
addressing parameters while the
block is active. The new
parameter are validated when
the previous job is closed.
S7-400: Dynamic modification
of address parameters is not
possible: the connection is
specified and fixed by the first
block call and remains
unchanged until the next
warm or cold restart.