Nor-Cal SDC15 Controller - Manual (Page 181)

8 - 3 Description of Commands
■ Read command (03H)
● Send Message
This is a command capable of reading the contents of continuous data addresses
from a specified read start data address with a single message. The following is an
example of send message while reading data:
MODBUS ASCII
(1) Start of message
(2) Station address
(3) Read command
(4) Start word address
(5) Read count
(6) Checksum (LRC)
(7) Delimiter
MODBUS RTU
(1) Station address
(2) Read command
(3) Start word address
(4) Read count
(5) Checksum (CRC)
● Response Message
A response message corresponding to the command content is returned when the
message is correctly received.
The figure below shows the structure of the response message while reading data.
MODBUS ASCII
• Example in case of normal reception
(1) Start of message
(2) Station address
(3) Read command
(4) Data count X 2
(5) Read data 1
(6) Read data 2
(7) Checksum (LRC)
(8) Delimiter
8-7
Chapter 8. MODBUS COMMUNICATIONS FUNCTIONS
(2) (1) (3) (4)
3AH
:
30H
0
41H
A
30H
0
33H
3
30H
0
33H
3
45H
E
39H
9
30H
0
30H
0
30H
0
32H
2
30H
0
35H
5
0DH
CR
0AH
LF
(5) (6) (7)
(2) (1) (3) (4)
0AH 03H 03H E9H 00H 02H 14H
(5)
C0H
(2) (1) (3) (4)
3AH
:
30H
0
41H
A
30H
0
33H
3
30H
0
34H
4
30H
0
33H
3
30H
0
31H
1
30H
0
30H
0
30H
0
33H
3
45H
E
38H
8
D0H
CR
0AH
LF
(5) (6) (7) (8)