SR05-D1A3-PV manual v1801 43/83
6.2 Network communication: function codes, registers, coils
Warning: Using the same Modbus address for more than one device will lead to irregular
behaviour of the entire network. This chapter describes function codes, data model and
registers used in the SR05-D1A3-PV firmware. Communication is organised according to
the specifications provided by the Modbus Organization. These specifications are
explained in the documents “Modbus application protocol v1.1b” and “Modbus over serial
line v1.02”. These documents can be acquired free of charge at www.modbus.org.
Table 6.2.1 Supported Modbus function codes
SUPPORTED MODBUS FUNCTION CODES
FUNCTION CODE (HEX) DESCRIPTION
0x01 Read Coils
0x02 Read Discrete Inputs
0x03 Read Holding Registers
0x06 Write Single Holding Register
0x08 Diagnostics
0x0F Write Multiple Coils
0x10 Write Multiple Registers
Note: In accordance with the Modbus application protocol specification function codes
0x01 to 0x06, 0x08, 0x0F and 0x10 belong to the category of public function codes,
whereas function code 0x46 belongs to the category of user defined function codes. User
defined function codes are non standard. The usage of function code 0x46 is explained in
detail in section 6.3.3.
Table 6.2.2 Modbus data model
MODBUS DATA MODEL
PRIMARY TABLES OBJECT TYPE TYPE OF
Discrete input Single bit R
Coil Single bit R/W
Holding register 16 bit word R/W
R = read only, W = write only, R/W = read / write
The instrument does not distinguish between discrete input and coil; neither between
input register and holding register.
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