Read Holding Registers (Function Code 03) - ProSoft Technology MVI56E-MNETC User Manual

Reference
User Manual
Node Func
Address Code
0B 02
The status of inputs 10197 to 10204 is shown as AC (HEX) = 10101 1100
(binary). Reading left to right, this show that inputs 10204, 10202, and 10199 are
all on. The other input data bytes are decoded similar.
Due to the quantity of input statuses requested, the last data field which is shown
as 35 HEX = 0011 0101 (binary) contains the status of only 6 inputs (10213 to
102180) instead of 8 inputs. The two left-most bits are provided as zeros to fill
the 8-bit format.

5.4.4 Read Holding Registers (Function Code 03)

Query
This function allows you to retrieve the contents of holding registers 4xxxx
(Modbus 4x range) in the addressed server. The registers can store the
numerical values of associated timers and counters which can be driven to
external devices. The addressing allows retrieving up to 125 registers at each
request; however, the specific server device may have restrictions that lower this
maximum quantity. The registers are numbered form zero (40001 = zero, 40002
= one, and so on). The broadcast mode is not allowed.
The example below reads registers 40108 through 40110 (three registers) from
server number 11.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display.
Node Function
Address Code
0B 03
Response
The addressed server responds with its address and the function code, followed
by the information field. The information field contains 1 byte describing the
quantity of data bytes to be returned. The contents of the registers requested
(DATA) are two bytes each, with the binary content right justified within each pair
of characters. The first byte includes the high order bits and the second, the low
order bits.
Page 138 of 172
Modbus TCP/IP Client Enhanced Communication Module - Client/Server
Byte Data Discrete
Count Input 10197 to
10204
03 AC
Data Start Data Start
Registers Registers Low
High
00 6B
MVI56E-MNETC/MNETCXT ♦ ControlLogix Platform
Data Discrete Data Discrete
Input 10205 to Input 10213 to
10212 10218
DB 35
Data Number Data Number
of Registers of Registers
High Low
00 03
Error Check
Field
(2 bytes)
CRC
Error Check
Field
(2 bytes)
CRC
ProSoft Technology, Inc.
September 20, 2018