Data Exchange Between Master And Plc Functionality (Cpu); Example Modbus Tcp Master And Plc Functionality (Cpu); Data Access By The Modbus Tcp Master; Data Access By The Plc Functionality - WAGO 750 Series Manual

76 • Fieldbus Controller 750-841
Data Exchange

3.1.6.6 Data Exchange between Master and PLC Functionality (CPU)

The fieldbus master and the PLC functionality of the controller regard the data
in a different manner.
Variable data created by the fieldbus master reaches the PFC as input
variables. Data created in the PFC is sent to the fieldbus master through
output variables.
In the PFC, the controller can access the MODBUS TCP PFC variable data
from word address 256 to 511 (double word address 128-255, byte address
512-1023) and the Ethernet IP PFC variable data from word address 1276 to
1531 (double word address 638-765, byte address 2552-3063).

3.1.6.6.1 Example MODBUS TCP Master and PLC functionality (CPU)

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).
BitNo = (Word * 16) + Bitno_in_Word
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP