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3 Product Overview
3 Product Overview
3.1
Modbus Protocol
The Modbus Application Protocol is an industrial communication protocol that is currently used in the solar sector
mainly for PV system communication. The Modbus protocol has been developed for reading data from or writing data
to clearly defined data areas. The Modbus specification does not prescribe what data is within which data area. The
data areas must be defined device-specifically in Modbus profiles. With knowledge of the device-specific Modbus
profile, a Modbus client (e.g. a SCADA system) can access the data of a Modbus server (e.g. SMA product with
Modbus interface).
The SMA Modbus profile and SunSpec Modbus profile are used for SMA products.
3.2
SMA Modbus Profile
The SMA Modbus profile contains definitions for SMA products. All available data on SMA products was assigned to
the corresponding Modbus registers for the definition. Not all SMA products support all Modbus registers of the
SMA Modbus profile.
3.3
System Topology
An SMA product with Modbus interface is connected with the SCADA system of the electric utility company or the grid
operator via Ethernet. The Modbus interface also enables communication via the Modbus protocol. From the
perspective of the Modbus protocol, an SMA product with Modbus interface constitutes a Modbus server that
supports the SMA Modbus profile.
3.4
Addressing and Data Transmission
3.4.1
Unit IDs
The Unit ID is a superordinate addressing type in the Modbus protocol.
The following tables shows the Unit IDs supported by this SMA product.
Unit ID
1
2
10+
3.4.2
Register Address, Register Width and Data Block
A Modbus register is 16 bits wide. For wider data items, connected Modbus registers are used and considered as
data blocks. The address of the first Modbus register in a data block is the start address of the data block.
3.4.3
Data Transmission
In accordance with the Modbus specification, only a specific volume of data can be transported in a single data
transmission in a simple protocol data unit (PDU). The data also contains function-dependent parameters such as the
function code, start address or number of Modbus registers to be transmitted. The amount of data depends on the
Modbus command used and has to be taken into account during data transmission (see Section 3.4.4, page 9).
With data storage in the Motorola format "Big Endian", data transmission begins with the high byte and then the low
byte of the Modbus register.
8
SMAModbus-ennexOS-TI-en-10
Explanation
This Unit ID is reserved for information on the SMA product.
This unit ID is reserved for the system parameters and measured values.
This unit ID refers to a device connected under unit ID 10 or higher whose data
are assigned to this unit ID.
SMA Solar Technology AG
Technical Information
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