Communication Via Function Blocks; Overview Of The Function Blocks - Siemens SIMATIC S7-400 Equipment Manual

Communication via Function Blocks

Introduction
Communication between the CPU, the CP 440 and a communication partner takes place via the
function blocks and the protocols of the CP 440.
Communication between CPU and CP 440
The function blocks form the software interface between the CPU and the CP 440. They must be
called in cycles from the user program.
Restriction in Multicomputing Operation
In multicomputing operation only one CPU can access the CP because communication between
the CPU and CP is not multicomputing-compatible.
Communication between CP 440 and a Communication Partner
The transmission protocol conversion takes place on the CP 440. The protocol is used to adpat
the interface of the CP 440 to the interface of the communication partner.
This enables you to link an S7 programmable logic controller with any communication partner
that can handle the ASCII driver and the 3964(R) procedure.
Calling the Function Blocks in Interrupt OBs
It is not permissible to simultaneously call a function block in OB1 and in the interrupt OB (time
OBs). The reason for this is that the function block cannot be called again if an interrupt OB
triggers an interruption. If you need to call the function block in OB1 and in the interrupt OB, you
must disable the interrupts (SFC 41) in the lower priority OB before the FB call and enable them
again after the FBs have executed.
6.1

Overview of the Function Blocks

Introduction
The S7-400 programmable logic controller provides you with a number of function blocks that
initiate and control communication between the CPU and the CP 440 communication processor
in the user program.
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE
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