Rtu Command Codes And Communication Data; Command Code 03H, Reading N Words (Continuously Up To 16 Words) - INVT Goodrive3000 Series Operation Manual

Goodrive3000 series medium voltage VFD

8.4 RTU command codes and communication data

8.4.1 Command code 03H, reading N words (continuously up to 16 words)

The command code 03H is used by the master to read data from the VFD. The count of data to be read depends on the
"data count" 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 running status of the VFD.
For example, to read two contiguous data content pieces from 0004H from the VFD with the address of 01H (that is, to
read content from data addresses 0004H and 0005H), the frame structure is as follows:
RTU master command (from the master to the VFD)
ADDR (address)
CMD (command code)
Start address MSB
Start address LSB
Data count MSB
Data count LSB
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.
ADDR=01H means the command message is sent to the VFD with the address of 01H and ADDR occupies one byte.
CMD=03H means the command message is sent to read data from the VFD and CMD occupies one byte.
"Start address" means reading data from the address and it occupies two bytes with the MSB on the left and LSB on the
right.
"Data count" indicates the count of data to be read (unit: word). "Start address" is "0004H" and "Data count" is 0002H,
indicating that data is to be read from the data addresses of 0004H and 0005H.
CRC check occupies two bytes, with the LSB on the left, and MSB on the right.
RTU slave response (from the VFD to the master)
Number of bytes
MSB of data in 0004H
LSB of data in 0004H
MSB of data in 0005H
LSB of data in 0005H
The response information is described as follows:
"ADDR" is "01H", indicating that the message is sent by the VFD whose address is 01H. The ADDR information occupies
START
CRC LSB
CRC MSB
END
START
ADDR
CMD
CRC LSB
CRC MSB
END
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
-197-
Moudbus protocol
01H
03H
00H
04H
00H
02H
85H
CAH
01H
03H
04H
13H
88H
00H
00H
7EH
9DH