Siemens Simatic S7 Series System Manual

Libraries
9.3 Modbus library instructions
S7-200 SMART
450 System Manual, 09/2015, A5E03822230-AC
LAD
Description
Network 6
Call the second MBUS_MSG instruction when the second
enable flag (M2.1) is ON. The First parameter must be set
for only the first scan that the instruction is enabled.
This instruction reads (RW = 0) 4 holding registers from
slave 2. The data is read from address 40010 - 40013 in the
Modbus slave and copied to VB200 - VB207 (4 words) in
the CPU.
Network 7
When the second MBUS_MSG instruction is complete
(Done goes from 0 to 1), clear the enable for the second
MBUS_MSG instruction.
If Error (MB1) is not zero, then set Q0.2 to show the error.
9.3.5
Modbus advanced user information
Overview
This topic contains information for advanced users of the Modbus RTU master library. Most
users should not need this information and should not modify the default operation of the
Modbus RTU master library.
Retries
The Modbus master instructions automatically resends the request to the slave device if one
of the following errors is detected:
● There is no response within the response timeout time (parameter Timeout on the
MBUS_CTRL) instruction (Error code 3).
● The time between characters of the response exceeded the allowed value (Error code 3).
● There is a parity error in the response from the slave (Error code 1).
● There is a CRC error in the response from the slave (Error code 8).
● The returned function did not match the request (Error code 7).
The Modbus Master resends the request two additional times before setting the Done and
Error output parameters.

Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.