Parity Check
Three check modes: Odd parity、even parity and no parity. The check mode can be set in the
programming mode.
Function code
According to the specific application of this instrument, only one function code ”03” is used, to
read the read holding registers. Other Modbus function code is not valid in this instrument.
Abnormal corresponding
According to the specific application of this instrument, three abnormal data are supported in the
RTU mode.
01: false function
02: false data address
03: false data
Electrical connection
The instrument supports the EIA/TIA-485 standard 2-wire communication link.
This instrument does not require polarity of the bias circuit.
The cable is suggested to be a pair of balanced twisted-pair cable, and shielded cable is best. When
the baud rate is 9600bit / s, maximum length of the cable (AWG26 specification and above) is
1000m.
The RTU mode
The RTU frame format: the representation of data is hexadecimal byte. Each byte has 11 bits: 1
start bit, 8 data bits, 1 parity check bit, 1 stop bit, 2 stop bits when without parity check.
1) The master request:
Address code + Function code + Data + CRC
(03H) (00H00H00H02H)
In the master request frame format, the value of “Function code ” and ”Data” are fixed.
And the address code is the hexadecimal values of the instrument’s address number.
Address code: The address of the receiver, in RTU mode it is coded with one
hexadecimal byte, which is corresponding to the decimal valid number (0-247).
Function code: the code is “03H”, because only one function code ”03” is used to read
the read holding registers.
Data: the data has 4 bytes, the first 2 bytes are the address of register to read, the last 2
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