So i want to send this code : 01 00 14 00 58 over ModBus RTU utilizing minimalmodbus to my VIRTUAL COM Port (COM2).
So i do get the "code" but i also get other bytes before and after the code and i can seem to know where they come from and how i can resolve it.
I did try to use another libary called pymodbus but i got the same result
PythonCode :
import serial
import minimalmodbus as mrtu
mrtu.BYTEORDER_BIG = 1
insmrt = mrtu.Instrument('COM2',1 ,mrtu.MODE_RTU,close_port_after_each_call= False,debug=True)
insmrt.precalculate_read_size= False
insmrt.clear_buffers_before_each_transaction= True
insmrt.serial.baudrate = 38400
insmrt.serial.bytesize = 8
insmrt.serial.parity = serial.PARITY_NONE
insmrt.serial.stopbits =1
insmrt.serial.timeout = 5
insmrt.handle_local_echo = None
def inscommmand():
#insmrt.write_string = "$0100140058"
insmrt.write_registers(0,[0x01,0x14,0x58])
while 1:
try:
inscommmand()
except:
continue
I don't really know what you are trying to do or what you mean exactly by send this code by Modbus but I'm afraid what the library (minimalModbus) is doing is exactly what it is supposed to.
If you call:
insmrt.write_registers(0,[0x01,0x14,0x58])
The library will build the following Modbus frame:
01 10 0000 0003 06 0001 0014 0058 9ABE
This is what each value on this frame means:
01: The Slave Address (default is address 1)
10: The Function Code 16 (Write Multiple Holding Registers, 16 = 10 hex)
0000: The address of the first register (0000 hex = 0, +40001 offset = register #40001).
0003: Number of registers to write since you are giving a 3-element list
06: Number of data bytes that follow (3 registers x 2 bytes each = 6 bytes).
0001: Value to write to register 40001
0014: Value to write to register 40002
0058: Value to write to register 40003
9ABE: The CRC (Cyclic Redundancy Check) for error checking.
The sequence 01 00 14 00 58 is not a valid Modbus frame because there is no function code 00(only values from 1 to 6, 15, and 16 are allowed).
Maybe what you want is just to send that sequence over the serial port? Otherwise, you should think about where those values are coming from.