Appendix B – Modbus Protocol
B-12
NMBA-01 Installation and Start-up Guide
Function Codes
The NMBA-01 supports three Modbus function codes. These allow the
Master to read and write 16-bit integer values to the drive.
03 Read Holding
Registers
Reads the binary contents of holding registers (4X references) in the
slave. Broadcast is not supported.
Query
The query message specifies the starting register and quantity of regis-
ters to be read. Registers are addressed starting at zero: registers 1–
16 are addressed as 0–15.
Here is an example of a request to read registers 40108–40110 from
slave device 17:
Figure B-5 Read Holding Registers - Query
QUERY
Field Name
Example
(Hex)
Slave Address
11
Function
03
Starting Address Hi
00
Starting Address Lo
6B
No. of Points Hi
00
No. of Points Lo
03
Error Check CRC
CRC (16-Bits)
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