Fieldbus Controller 750-841 • 69
Data Exchange
Addressing Example:
Address calculation (depending upon the word address):
Bit address: |
word address .0 to .15 |
|
Byte address: |
1. |
Byte: 2 x word address |
|
2. |
Byte: 2 x word address + 1 |
Dword address: |
word address (even numbers) / 2 |
|
|
or |
word address (uneven numbers) / 2, rounded off |
3.1.5.3 Data Exchange between MODBUS TCP Master and I/O Modules
The data exchange between the MODBUS TCP master and the I/O modules is made via the Ethernet Fieldbus port using MODBUS TCP read and write commands.
The controller handles four different types of process data with MODBUS TCP:
•Input words
•Output words
•Input bits
•Output bits
The relationship between bits and words are defined in the table below:
Digital inputs/outputs |
16. |
15. |
14. |
13. |
12. |
11. |
10. |
9. |
8. |
7. |
6. |
5. |
4. |
3. |
2. |
1. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
Prozess data word |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
Bit |
|
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
||
|
|||||||||||||||||
Byte |
High-Byte |
|
|
|
|
|
|
Low-Byte |
|
|
|
|
|
|
|||
D1 |
|
|
|
|
|
|
|
D0 |
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
Table 3.9: Allocation of Digital Inputs/Outputs to Process Data Word in Intel Format
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
70 • Fieldbus Controller 750-841
Data Exchange
Adding an offset of 0x0200 to the MODBUS output address lets you read back output data.
Note
For MODBUS mapping, all output data over 256 words resides in the memory area 0x6000 to 0x62FC, and can be read back with an offset of 1000hex (0x1000) added onto the MODBUS address.
|
MODBUS master |
||
0x0000 |
0x6000 |
0x0000 |
0x6000 |
|
|
(0x0200) |
(0x7000) |
|
PII |
|
PIO |
|
|
00x0FF |
0x62FC |
0x00FF |
0x62FC(0x02FF) |
(0x72FC) |
|
Inputs |
|
|
Outputs |
|
I/O modules |
|
|
|
|
|
PII = Process Input |
|
|
|
Image |
|
|
|
PIO = Process Output |
|
|
|
Image |
Programmable Fieldbus Controller
Fig. 3-9: Data exchange between MODBUS master and I/O modules |
g015045e |
The MODBUS register assignments allow for a Fieldbus Master to read and write data from the controller. The register mapping for IEC 61131.1 varies from the MODBUS assignments. Please refer to section 3.1.5.6.2 for a comparison of MODBUS TCP and IEC 61131.1 address mapping.
WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP
Fieldbus Controller 750-841 • 71
Data Exchange
3.1.5.4 Data Exchange between Ethernet IP Master and I/O Modules
Data exchange between the Ethernet IP master and the I/O modules is object oriented. Each node in the network is represented as a collection of objects. The “assembly” object defines the structure of objects for data transfer. With the assembly object, data (e.g. I/O data) can be grouped into blocks (mapped) and sent via a single communication link. As a result of this mapping technique, fewer access operations to the network are required.
Input and output assemblies have different functions.
An input assembly reads data from the application over the network or produces data on the network.
Where as, an output assembly writes data to the application or consumes data from the network.
Various assembly instances are permanently pre-programmed in the fieldbus controller (static assembly).
After switching on the power supply, the assembly object maps data from the process image. As soon as a connection is established, the master can address the data with "class", "instance" and "attribute" and access or read and/or write the data via I/O links.
The mapping of the data depends on the chosen assembly instance of the static assembly.
Further information
The assembly instances for the static assembly are described in the section
7.3.2.6 "Assembly (04 hex)".
WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP
72 • Fieldbus Controller 750-841
Data Exchange
3.1.5.5 Data Exchange between PLC Functionality (CPU) and I/O Modules
Through absolute addresses, the PLC functionality of the controller can directly address the I/O module data.
The PFC addresses the input data with absolute addresses. The data can then be processed, internally in the controller, through the IEC 61131-3 program, whereby the flags are filed in a permanent memory area. Following this, the linking results can be directly written in the output data via absolute addressing.
Inputs |
|
|
Outputs |
|
I/O modules |
750-4xx....6xx |
|
%IW0 |
%IW512 |
%QW0 |
%QW512 |
|
PII |
|
PIO |
%IW255 |
%IW1275 |
%QW255 |
%QW1275 |
Inputs |
|
|
Outputs |
PLC functionality (CPU) |
|||
|
|
|
PII = Process Input |
|
|
|
Image |
|
|
|
PIO = Process Output |
|
|
|
Image |
Programmable Fieldbus Controller
Fig. 3-10: Data exchange between PLC functionality (CPU) and I/O modules 15043e
WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP