Function Block Modbuscp; Functionality Of The Fb - Siemens SIMATIC S7 Manual

5

Function Block MODBUSCP

5.1

Functionality of the FB

General
Information
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
The function block MODBUSCP allows a communication between a CP443-1
and CP 343-1 and a partner, which supports Open MODBUS/TCP protocol.
The function codes 1, 2, 3, 4, 5, 6, 15 and 16 are supported.
Depending on the parameterization the FB can be operated both in client and
in server mode. It is also possible to operate a CP as a client and as a server
at the same time. In this case two NetPro connections and 2 FB calls are
necessary. In the operating mode server the functionality multitasking,
according to the MODBUS reference, is not implemented.
There is no limitation of the maximum number of parallel called modbus
blocks on the part of the library. Though it depends on the CPU and CP how
many AG functions can run simultaneously. The maximum number of AG
calls can be taken from the manual of the CPU: "Technical Data" >
"Communication". In the manual of the CP it's detailed, how many
AG_SEND/AG_RECV or AG_LSEND/AG_LRECV can be processed by this
CP simultaneously.
The block MODBUSCP calls the blocks MB_CPCLI (FB106) and MB_CPSRV
(FB107) internally. The block MB_CPCLI comprises the function of Modbus
client, the block MB_CPSRV executes the function of Modbus server.
The function block performs the following functions:
•
Calls the standard functions for the data transfer between the CPU
and the CP
•
Generates MODBUS specific telegram header before send
•
Verification of the MODBUS specific telegram header after receive
•
Verification if the memory areas exist which are requested by the
client
•
Generate exception telegrams when failures occur (only when CP is
in server mode)
Exception
code
1
2
3
Meaning
The requested function code is not supported.
An access to a not existing or not permitted address
was carried out.
An invalid length was indicated for this function code.
Function Block MODBUSCP
5-1