Siemens SIMATIC S7-1200 System Manual page 1207

Hide thumbs Also See for SIMATIC S7-1200:

Function manual (527 pages)

Manual (364 pages)

System manual (338 pages)

page of 1614

/ 1614
Contents
Table of Contents
Bookmarks

Table of Contents

Modbus communication function codes (1, 2, 4, 5, and 15) can read and write bits and words

directly in the input process image and output process image of the CPU. For these function

codes, the MB_HOLD_REG parameter must be defined as a data type larger than a byte.

The following table shows the example mapping of Modbus addresses to the process image

Table 13- 82 Mapping of Modbus addresses to the process image

Read words Input

Modbus communication function codes (3, 6, 16) use a Modbus holding register which can

be an M memory address range or a data block. The type of holding register is specified by

the MB_HOLD_REG parameter on the Modbus_Slave instruction.

MB_HOLD_REG data block type

A Modbus holding register data block must allow both direct (absolute) and symbolic

addressing. When you create the data block the "Standard" access attribute must be

The following table shows examples of Modbus address to holding register mapping that is

used for Modbus function codes 03 (read words), 06 (write word), and 16 (write words). The

actual upper limit of DB addresses is determined by the maximum work memory limit and M

memory limit, for each CPU model.

Table 13- 83 Mapping of Modbus addresses to CPU memory

Modbus master

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

Modbus functions

Address range

Communication processor and Modbus TCP

Output Process Image

Input Process Image

Input Process Image

Output Process Image

Output Process Image

MB_HOLD_REG parameter examples

13.5 Modbus communication

Q0.0 to Q1023.7

I0.0 to I1023.7

IW0 to IW1022

Q0.0 to Q1023.7

"Recipe".ingredient

"Recipe".ingredient[1]

"Recipe".ingredient[2]

"Recipe".ingredient[3]

"Recipe".ingredient[4]

"Recipe".ingredient[5]

Siemens SIMATIC S7-1200 System Manual page 1207

Related Manuals for Siemens SIMATIC S7-1200

Related Products for Siemens SIMATIC S7-1200

Table of Contents