750-841 WAGO, 750-841 Datasheet - Page 73

• Manufacturer Part Number: 750-841
• Description: CONTR.ETHERNET TCP/IP 10/100MBIT
• Manufacturer: WAGO

Specifications of 750-841

• Rohs Compliant: YES
• No. Of Digital Inputs: 10
• No. Of Digital Outputs: 10

3.1.6.6.1 Example MODBUS/TCP Master and PLC functionality (CPU)
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
Data Access by the MODBUS/TCP Master
With MODBUS TCP, the fieldbus master can access controller data as words
or bits.
When accessing the first 256 words of memory from the Fieldbus port
(physical I/O modules), the I/O modules start with the address 0 for both bit
and word access.
When accessing data from the starting memory address of 256, the bit and
word addresses follow the sequence below:
4096 for bit 0 in word 256
4097 for bit 1 in word 256
...
8191 for bit 15 in word 511.
The bit number can be calculated from the following formula:
Data Access by the PLC Functionality
When accessing the same data from both a PLC and Fieldbus master, the
following memory address conventions should be understood:
A 16 bit IEC 61131-3 variable uses the same addressing as the MODBUS
word format.
An IEC 61131-3 boolean variable (1 bit) uses a “WORD.BIT” notation for
addressing, which is different from MODBUS’s bit notation.
The “WORD.BIT” notation is composed of the boolean’s word address and
bit number in the word, separated by a dot. The Word and Bit values are zero
based (e.g., %IX0.0 is the first possible digital input).
Example:
MODBUS bit number 19 => bit addressing in PLC <Wordno>.<Bitno> = 1.2
The PLC functionality of the PFC can also access the data as Bytes and
Double- Words.
The byte addresses are computed according to the following formula:
The double word address is computed according to the following formula:
More information
You can find a detailed description of the MODBUS addressing and the
correspondent IEC61131-addressing in the chapter „MODBUS Register
Mapping“.
Double word address = High word address/2 (rounded off)
BitNo = (Word * 16) + Bitno_in_Word
High-Byte Address = Word address*2
Low-Byte Address = (Word address*2) + 1
or = Low word address/2
Fieldbus Controller 750-841
Fieldbus Controller
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