Siemens Simatic S7 Series System Manual

Libraries
9.3 Modbus library instructions
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
449
The following program turns on outputs Q0.1 and Q0.2 if there is an error returned from the
MBUS_MSG instruction.
Table 9- 33 Example Modbus master program
LAD
Description
Network 1:
Initialize and monitor the Modbus master by calling
MBUS_CTRL on every scan. The Modbus master is set for
9600 baud and no parity. The slave device is allowed 1000
milliseconds (1 second) to respond.
Network 2
On the first scan, reset the enable flags (M2.0 and M2.1)
used for the two MBUS_MSG instructions.
Network 3
When I0.0 changes from OFF to ON, set the enable flag for
the first MBUS_MSG instruction (M2.0).
Network 4
Call the MBUS_MSG instruction when the first enable flag
(M2.0) is ON. The First parameter must be set for only the
first scan that the instruction is enabled.
This instruction writes (RW = 1) 4 holding registers to
slave 2. The write data is taken from VB100-VB107
(4 words) in the CPU and written to address 40001 - 40004
in the Modbus slave.
Network 5
When the first MBUS_MSG instruction is complete
(Done goes from 0 to 1), clear the enable for the first
MBUS_MSG and set the enable for the second
MBUS_MSG instruction.
If Error (MB1) is not zero, then set Q0.1 to show the error.

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.