Modbus function reference
Modbus Function Code 03 — Read Holding Registers
Read 16-bit read/write register values
03
Read 16-bit read/write register values
Data model
Holding registers (4xxxx reference family)
Access
Read 16-bit read/write register values
Protocol quantity
1–125 registers
Worked example
Read two holding registers from protocol address 0. The response contains values 1250 and 678.
Typical use: Polling setpoints, configuration, commands and process values mapped in the holding-register table.
Request PDU
03 00 00 00 02Normal response PDU
03 04 04 E2 02 A6PDU examples omit the Modbus TCP MBAP header and the Modbus RTU unit-address/CRC envelope. Multi-byte values are shown in network byte order.
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