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 PLCÆPC(OK) PLCÆPC(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 02HStart
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
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