Data And Standard Functions Used By The Fb - Siemens SIMATIC S7 Manual
Open modbus / tcp
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5.4
Data and Standard Functions used by the FB
Instance DB
Local Variables
Timers
Flags
Standard FCs for
Data Transfer
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
The function block MODBUSCP stores its data in an instance DB. This
instance DB is created by STEP7 at the first call of the FB.
The instance data block contains parameters of type Input, Output,
Input/Output as well as static variables that it needs for its execution. These
variables are non-volatile and keep its validity between FB calls. The
variables control the internal process flow of the FB.
Required memory of the instance-DBs:
Instance-DB
work memory
MODBUSCP
ca. 1kByte
The FB requires 80 Bytes of local variables. Additionally the subordinate FBs
require local variables: FBs MB_CPCLI (30 byte) or MB_CPSRV (30 byte).
V1.x: AG_SEND/AG_RECV or AG_LSEND/AG_LRECV require, up to 58
bytes, depending on the used function block. That gives a maximum of 168
bytes of local data for a FB MODBUSCP V1.x-call.
V2.x: The function AG_CNTRL requires 178 bytes local data. That gives a
maximum of 288 bytes of local data for a FB MODBUSCP V2.x-call.
The function block does not use any timer.
The function block does not use any flag.
The function blocks MB_CPCLI and MB_CPSRV respectively called by FB
MODBUSCP use the blocks AG_SEND/AG_RECV (S7-300) and
AG_LSEND/AG_LRECV (S7-400) from the SIMATIC_NET library for the data
transfer between CPU and CP.
The blocks MODCLI and MODSRV version 2.x use the block AG_CNTRL
additionally to reset and reestablish the connection in case of error.
The following versions of the FCs are tested with FB MODBUSCP and
released for the communication:
S7-300:
FC5 "AG_SEND" version 4.2
FC6 "AG_RECV" version 4.7
FC10 "AG_CNTRL" version1.0
S7-400
FC50 "AG_LSEND" version 3.1
FC60 "AG_LRECV" version 3.1
FC10 "AG_CNTRL" version 1.0
Function Block MODBUSCP
load memory
ca. 2kByte
5-15
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