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5. The character P can be added before every basic command. It means that the transmitted data
has CRC verification. The verification method is to add all data back to the data that is cumulative
and binary and the 8-bit binary data is taken.
For example, the return information of the RT (cr) (lf) is : +1234567E+0m3 (cr) (lf), (the relative
binary system data is : 2BH, 31H, 32H, 33H, 33H, 34H, 35H, 36H, 37H, 45H, 2BH, 30H, 6DH,
20H, 20H, 0DH, 0AH).
The
sum
of
all
36H+37H+45H+2BH+30H+6DH+33H +20H=2F7, the low 8-bit data of its binary is F7. Therefore,
the data of the order PRT (cr) (lf) is called + 1234567E + 0m3!F7 (cr) (lf), "!" For delimiters, the
preceding character is the character of summation, followed by a check code of 1 byte.
6. Use of prefix W: W + numeric string address code + basic command. The numeric string value
range is 0 ... 255, except 13 (0DH carriage return), 10 (0AH line feed). If the instantaneous
velocity of flow meter no. 123 is to be accessed, the command W123DV (cr) (lf) can be issued.
The corresponding binary code is 57H, 31H, 32H, 33H, 44H, 56H, 0DH, 0AH; only the same
device with the same address of the Internet address and command will return the data.
7. W and P commands can be used in combination, for example W123PRT +. This means that
the device reading the network address is the cumulative value of the device with 123 and its
return data has eight accumulations and checksums. "s" expresses ON or OFF or UD. For
example, "TR:ON, RL:ON" expresses that the OCT and relay are in an actuated state; "TR:UD，
RL:UD" expresses that the OCT and relay are not actuated.
10.4.2
MODBUS-I communication protocol
This MODBUS-I protocol uses RTU transmission mode. The verification code uses CRC-16-IBM
(polynomial is X16+X15+X2+1, shield character is 0xA001) gained by cyclic redundancy
algorithm method. MODBUS-I-RTU mode uses hexadecimal numbers for data transmission.
1. Function code and format of the MODBUS-I protocol
The flow meter protocol supports the following two MODBUS function codes
Function code
its
return
data
0x03
0x06
© PCE Instruments
is
=2BH+31H+32H+33H+34H+34H+35H+
Performance data
Read register
Write single register
39
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