Watlow CLS200, MLS300 and CAS200 - Manual (Page 37)

Chapter 2: Modbus-RTU Protocol
Communications Specification 31
Examples
Read Examples
The data read must be sequentially located. If you’re reading a coil
rather than a register, you must offset the address by the location of the
bit you wish to read.
Sample Packet for Host Transmission
Sample Packet for Slave Transmission
Example
Slave
Address
in Hex
Function
in Hex
Start
Address
High
in Hex
Start
Address
Low
in Hex
Number
of Points
High
in Hex
Number
of Points
Low
in Hex
CRC
High
in Hex
CRC
Low
in Hex
1. Reading
PV of loop 2
(1600),
controller 1
(single-point
read) 01 03 01 6C 00 01 45 EB
2. Reading
loops 4 and 5
heat outputs,
of controller 3
(multipoint
read) 03 03 01 D1 00 02 94 2C
3. Reading
digital input
4, controller 1
(input status
read) 01 02 03 82 00 10 D9 AA
Example
Slave
Address
in Hex
Function
in Hex
Byte
Count
in Hex
Data
in Hex
CRC
High
in Hex
CRC
Low
in Hex
1. Reading PV of loop 2 (1600),
controller 1 (single-point read) 01 03 02 3E 80 84 1B
2. Reading loops 4 and 5 (50%,
60%) outputs (heat), of controller 3
(multipoint read) 03 03 04 3F DE 4C 4A 2D 41
3. Reading digital input 4, controller
1 (input status read) 01 02 02 08 00 BE 78