ICP DAS USA ET-2242, User Manual

Page: 74 / 99

ET-2200 Series Ethernet I/O Modules
Copyright © 2016 ICP DAS CO., Ltd. All Rights Reserved. - 74 -

RTU Data Structure
Byte 06 Byte 07 Bytes 08 - 09 Bytes 10 - 11
Net ID
(Station Number)
Function Code
Data Field
Reference Number
(Address Mapping)
Number of Points

Net ID specifies the address of the receiver (Modbus/TCP slave).

Function Code specifies the message type.

Data Field is the data block.
Net ID (Station Number)
The first byte in the frame structure of a Modbus RTU query
is the re ei er s address.
A valid
address is in the range of 0 to 247. Address 0 is used for general broadcast, while addresses 1 to 247
are given to individual Modbus devices.
Function Code
The second byte in the frame structure of a Modbus RTU query is the function code, which
describes what the slave device is required to do. Valid function codes are between 1 and 255. To
answer the query, the slave device uses the same function code as contained in the request. The
highest bit of the function code will only
e set to
if an error occurs in the system. In this way,
the master will know whether the message has been transmitted correctly or not.
Section Code Function
Reference
(Address)
6.2.1 01 (0x01) Read the Status of the Coils (Readback DOs) 0xxxx
6.2.2 02 (0x02) Read the Status of the Input (Reads DIs) 1xxxx
6.2.3 03 (0x03) Read the Holding Registers (Readback AOs) 4xxxx
6.2.4 04 (0x04) Read the Input Registers (Reads AIs) 3xxxx
6.2.5 05 (0x05) Force a Single Coil (Writes DO) 0xxxx
6.2.6 06 (0x06) Preset a Single Register (Writes AO) 4xxxx
6.2.7 15 (0x0F) Force Multiple Coils (Writes DOs) 0xxxx
6.2.8 16 (0x10) Preset Multiple Registers (Writes AOs) 4xxxx
ГК Атлант Инжиниринг – официальный представитель в РФ и СНГ
+7(495)109-02-08 sales@bbrc.ru www.bbrc.ru