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.
Run the reference
Compose the request publicly, then use Pro for advanced graded exceptions, saved fixtures, complete history and project sharing.
Industrial communications path
Choose the physical layer, frame the request, inspect the mapped data and diagnose exception evidence in one connected sequence.