Chapter 2 Basic Unit Specification
3. Communication ports
2-16
D.
03H read register:
Function
Code
03H
Function
This function code is used to read the contents of from 1 to 125 consecutive blocks of
holding registers in a remote device.
Format
PC
Æ
PLC
PLC
Æ
PC(OK) PLC
Æ
PC(ERROR)
Slave Address
01H
Slave Address
01H
Slave Address
01H
Function Code
03H
Function Code
03H
Function Code 83H
High 40H
Bytes
06H
Exception
Code 02H
Start
Address Low 6BH
*Responding
Data
Low C1H
High 00H
Low
XX
CRC-16
High 34H
Data
Register
number Low 03H
CRC-16
High
XX
Low 63H
CRC-16
High 47H
Remark
1.
Start character is the first register address.
2.
Byte count equals quantity of register ×2. Data length is byte count. For each
register, each word contains a high byte and a low byte.
3.
The data length is equal to Bytes. As in the above example, Bytes=6, that is input
data length is 6 bytes.
4.
It is recommended to set the start address equal multiple of 8. It can improve the
program efficiency.
5.
XX represents that the data differs with different input data
