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VIPA System 300S
6.4.7 Modbus Slave - Communication with the user program
Overview
Installation
Communication principle
Reaction time
HB130 | CP | 341-1CH01 | en | 18-40
n
For the processing of the connecting jobs at slave side a user program is necessary
in the CPU.
n
The data transfer between CP and CPU happens by the Modbus communication FB
80 - MODB_341.
–
By this FB 7 - P_RCV_RK and FB 8 - P_SND_RK are called internally.
n
For communication at the slave side it is necessary to integrate FB 7 - P_RCV_RK
and FB 8 - P_SND_RK to the project.
n
Every for the Modbus communication FB 80 relevant data are located in an instance
DB. This DB is the instance DB for the internally called blocks at the same time.
Access to the instance DB is permitted only as read-only.
CAUTION!
–
Calling of the FB 80 - MODB_341 within diagnostic or process inter-
rupt is not allowed.
–
Please regard the FB does not have a parameter check; which
means that if there are invalid parameters, the CPU may switch to
STOP mode.
1.
The function block FB 80 is installed together with the protocol driver.
2.
If not already happen, finish the Siemens SIMATIC manager, start the installation
file of the driver and follow the instructions.
3.
FB 80 - MODB_341 may be found in the block library after installation.
4.
The library may be opened in the Siemens SIMATIC manager by 'File è Open
è Libraries' and here "Modbus".
n
By a cyclic call of the FB 80 - MODB_341 request telegrams from the master may be
received and data may be sent with the slave CP.
n
The conversion of the corresponding Modbus address to the memory area of the
CPU is made by the CP.
n
The memory area allocation happens by the parameterization within the hardware
configuration.
n
The FB 80 - MODB_341 is described below.
MODB_341' page 74
For the write function codes (FC 05, FC 15) is valid:
n
Reaction time = AG cycle + time CP ® CPU + time CPU ® CP
–
n
For the other function codes is valid:
Reaction time = time CP ® CPU + time CPU ® CP
–
n
The CP does not send the reply message to the master system until after the data
transfer CPU ® CP.
–
In this instance the standard reply monitoring time of 2s can be kept.
Modbus > Modbus Slave - Communication with the user program
Ä Chap. 6.4.7.1 'Send data FB 80 -
Communication protocols
73
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