Shihlin electric SPM-3 User Manual

_________________________Shihlin Electric SPM-3 User Guide__________________
20
Master
Slave 1
Slave 2
Slave 3
Slave n
Q
uery
Res
p
onse
5.2 Modbus
At the start of modbus communication, master will issue a “Query” to the slave. Every slave will monitor
the “Query” address, if a “Query” belongs to a slave, the slave will “execute” and send back a
“response” to the master
5.2.1 Modbus Format
The Query-Response Cycle
Query message from Master
Device Address
Function Code
8 bit Data Bytes
Error Check
Response messages from Slave
5.3 Communication protocol
SPM-3 use Modus RTU as the communication protocol, and function codes are 0x03, 0x04, and 0x10.
The following charts show the master’s “Query” and slave’s “Response” format.
Query：
Slave
Address
Function
Code
0x03,
0x04
Start
Address
(Hi)
Start
Address
(Lo)
Number
of Points
(Hi)
Number
of Points
(Lo)
Error
Check
(Lo)
Error
Check
(Hi)
Response：
Slave
Address
Function
Code
0x03,
0x04
Byte
Count
Data
(Hi)
Data
(Lo)
Error
Check
(Lo)
Error
Check
(Hi)
Device Address
Function Code
8 bit Data Bytes
Error Check

Shihlin electric SPM-3 Specifications

General

Brand	Shihlin electric
Model	SPM-3
Category	Measuring Instruments
Language	English