Siemens SIMATIC S7 Manual page 28

Call of the FB
Start-up of the FB
Cyclical Operation
of the FB
OB121
"Programming
Error"
!
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
For a correct program sequence the function block MODBUSPN has to be
called in 3 organization blocks:
•
OB100 Start-Up
•
OB121 Programming Error
•
Cyclic OB (OB1 or cyclic interrupt OB, e.g. OB35)
The subordinate blocks of the Modbus library MOD_CLI, MOD_SERV and
TCP_COMM must not be called additionally in an organization block.
A coexistent call of FB MODBUSPN in OB1 and a cyclic interrupt OB, e.g.
OB35 is not permissible.
The Modbus block must be called in OB121. You will find more information
regarding this matter in section 5 "Licensing".
The function block MODBUSPN is unconditionally called once in OB100.
•
The initialization parameters must be set according to the station
configuration.
•
The initialization parameters are copied into the instance DB.
•
The runtime parameters are not evaluated during the start-up.
•
The values of the parameter data block MODBUS_PARAM are
evaluated.
In case of cyclical operation, the FB MODBUSPN is called in OB1 or in a
cyclic interrupt OB.
•
Corresponding to the runtime parameters, the functions of the
function block are activated.
•
While a request is being processed, changes to the runtime
parameters are ignored.
•
In the cyclical operation mode, initialization parameters are ignored.
The block MODBUSPN must be called in OB121 with the same instance DB
as in the start-up OB and the cyclic OB.
If the block has not been licensed yet, the OB121 is called.
_____________________________________________________________
Warning
The CPU will turn to STOP mode, if the OB121 is not available.
_____________________________________________________________
The call of MODBUSPN in OB121 executes an entry in the diagnostic buffer,
which points out that the registration key is missing. The LED SF or INTF of
the CPU flashes simultaneously.
Function Block MODBUSPN
6-2