Rtu Command Code And Communication Data - Hitachi S1 Series Basic Manual

S1 series standard inverter
content in the frame. The program of this method is simple, and the calculation is fast, but the ROM
space occupied is large. Use this program with caution in scenarios where there are space
occupation limits on programs.

9.4 RTU command code and communication data

9.4.1 Command code: 03H, reading N words (continuously reading a maximum of 16 words)
The command code 03H is used by the master to read data from the inverter. The quantity of data to
be read depends on the "data quantity" in the command. A maximum of 16 pieces of data can be read.
The addresses of the read parameters must be contiguous. Each piece of data occupies 2 bytes, that
is, one word. The command format is presented using the hexadecimal system (a number followed by
"H" indicates a hexadecimal value). One hexadecimal value occupies one byte.
The 03H command is used to read information including the parameters and operation state of the
inverter.
For example, starting from the data address of 0004H, to read two contiguous pieces of data (that is,
to read content from the data addresses 0004H and 0005H), the structure of the frame is described in
the following table.
RTU master command (transmitted by the master to the inverter)
START
ADDR (address)
CMD (command code)
Most significant byte (MSB) of
the start address
Least significant byte (LSB) of
the start address
MSB of data quantity
LSB of data quantity
LSB of CRC
MSB of CRC
END
The value in START and END is "T1-T2-T3-T4 (transmission time of 3.5 bytes)", indicating that the
RS485 needs to stay idle for at least the transmission time of 3.5 bytes. An idle time is required to
distinguish on message from another to ensure that the two messages are not regarded as one.
The value of ADDR is 01H, indicating that the command is transmitted to the inverter whose address
is 01H. The ADDR information occupies one byte.
The value of CMD is 03H, indicating that the command is used to read data from the inverter. The
CMD information occupies one byte.
"Start address" indicates that data reading is started from this address. It occupies two bytes, with the
MSB on the left and LSB on the right.
"Data quantity" indicates the quantity of data to be read (unit: word).
T1-T2-T3-T4 (transmission time of 3.5 bytes)
CAH
T1-T2-T3-T4 (transmission time of 3.5 bytes)
-184-
01H
03H
00H
04H
00H
02H
85H