Data And Standard Functions Used By The Fb - Siemens SIMATIC S7 Manual

6.4

Data and Standard Functions used by the FB

Instance DB
Local Variables
Parameter DB
Timers
Flags
Standard FBs for
Connection
Handling
Standard FBs for
Data Transfer
MODBUSPN:
SFCs for
Miscellaneous
Functions
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
The function block MODBUS stores its data in an instance DB. This instance
DB is created by STEP7 when initially calling the FB.
The instance data block contains parameters of the types input, output and
input/output as well as static variables required for its execution. These
variables are remanent and keep their validity between FB calls. The
variables control the internal process flow of the FB.
Required memory of the instance-DBs:
Instance-DB work memory
MODBUSPN 830 Byte
The FB requires 96 bytes of local variables. Additionally, MOD_CLI (110 Byte)
or MOD_SERV (84 Byte) and TCP_COMM require 2 bytes local variables and
TCON, TDISCON, TSEND or TRCV use up to 28 bytes depending on the
used function block. That is a total of max. 236 bytes of local data for one FB
MODBUSPN call.
The connection- and Modbus-specific parameters are stored in the parameter
data block MODBUS_PARAM.
The FB does not use any timers.
The function block does not use any flags.
The function block TCP_COMM, called by MODBUSPN, uses the blocks
TCON and TDISCON of the standard library to establish and terminate the
connection between the PLC and the communication partner.
The function block TCP_COMM, called by MODBUSPN, uses the blocks
TSEND and TRCV of the standard library for the data transfer between the
PLC and the communication partner.
The FB MODBUSPN uses the following SFCs from the standard library:
•
FC10 "EQ_STRING"
•
SFC6 "RD_SINFO"
•
SFC20 "BLKMOV"
•
SFC24 "TEST_DB"
•
SFC51 "RDSYST"
•
SFC52 "WR_USMSG"
Function Block MODBUSPN
load memory
1852 Byte
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