Hello ,
I have this C# function that work as a checksum
public static byte gen(byte[] p)
{
byte lcs = 0;
foreach (byte b in p)
{
lcs += b;
}
lcs = (byte)(0 - lcs);
return lcs;
}how can I change it to work in python?
Example I have this value in DEC:
48,51,50,51,3
the sum is 203 (which is CB in Hex)
so I need it to return 100-CB = 35
then break the 35 into 2 numbers: 3,5 -->so it will send byte 51,53
Thanks ,
I've got this
>>> d = bytes([48,51,50,51,3])
>>> str(256 - sum(d)).encode('ascii')
b'53'
#!/usr/bin/python3
def gen(p):
lcs = 0
for b in p:
lcs += b
lcs %= 256
lcs = 256 - lcs
return lcs
rc1 = gen([48,51,50,51,3])
print("rc1=", rc1)
rc2 = "%x" % rc1
print("rc2=", rc2)
d1 = ord(rc2[0])
d2 = ord(rc2[1])
print("d =", d1, d2)rc1= 53
rc2= 35
d = 51 53
Thanks ,
it working
Now I need to see how to combine it insdie the main code :
this is what I did :
import serial # import the module
def gen(p): #The CheckSum Function
lcs = 0
for b in p:
lcs += b
lcs %= 256
lcs = 256 - lcs
return lcs
COM_PortName = ('/dev/ttyUSB0')
COM_Port = serial.Serial(COM_PortName) # open the COM port
print('\n ',COM_PortName,'Opened')
COM_Port.baudrate = 4800 # set Baud rate
COM_Port.bytesize = 8 # Number of data bits = 8
COM_Port.parity = 'N' # No parity
COM_Port.stopbits = 1 # Number of Stop bits = 1
COM_Port.setDTR(0) #DTR=0,~DTR=1 so DE = 1,Transmit mode enabled
COM_Port.setRTS(0) #RTS=0,~RTS=1 (In FT232 RTS and DTR pins are inverted)
#this is an example of what need to be send :
#data = bytearray(b'\x02\x30\x33\x32\x33\x03\x33\x35') # Convert Character to byte array
#
SOF = bytearray(b'\x02')
SignAdd = bytearray(b'\x30\x33')
MSG = input('\n Enter Number - ')
EOF = bytearray(b'\x03')
rc1 = gen([SignAdd,MSG,EOF])
print("rc1=", rc1)
rc2 = "%x" % rc1
print("rc2=", rc2)
d1 = ord(rc2[0])
d2 = ord(rc2[1])
print("d =", d1, d2)
NoOfBytes = COM_Port.write(SOF) # Write data to serial port
NoOfBytes = COM_Port.write(SignAdd)
NoOfBytes = COM_Port.write(MSG)
NoOfBytes = COM_Port.write(d1,d2)
print('\n message was - ',MSG)
COM_Port.close() # Close the Serial port
dummy = input() # press any key to close in the input I only put numbers 0-99
but I get error from the gen function:
TypeError: unsupported operand type(s) for +=: 'int' and 'bytearray'
what is the mistake?
Thanks ,
if the answer could be with en explain , So I will learn it will be great :-)
I do not have a serial port,
so I write the output to a binary file.
I hope, this helps you.
!/usr/bin/python3
def gen(bytes):
lcs = 0
for b in bytes:
lcs += b
lcs %= 256
lcs = 256 - lcs
return lcs
COM_PortName = 'serial.txt'
COM_Port = open(COM_PortName, "wb")
SOF = b'\x02'
SignAdd = b'\x30\x33'
MSG = input('\n Enter Number - ').encode()
EOF = b'\x03'
rc1 = gen(SignAdd + MSG + EOF)
rc2 = "%02x" % rc1
NoOfBytes = COM_Port.write(SOF)
NoOfBytes = COM_Port.write(SignAdd)
NoOfBytes = COM_Port.write(MSG)
NoOfBytes = COM_Port.write(rc2.encode())
print('\n message was - ',MSG)
COM_Port.close()
#done
Quote:if the answer could be with en explain , So I will learn it will be great :-)
We don't know what p means when it enters gen(). Can you
print(repr(p)) at the beginning of the gen() function and post the output here?
not working
this is the code now:
import serial # import the module
def banner_bottom():
print(' +-------------------------------------------+')
print(' | Press Any Key to Exit |')
print(' +-------------------------------------------+')
def gen(p):
print(repr(p))
lcs = 0
for b in p:
lcs += b
lcs %= 256
lcs = 256 - lcs
return lcs
COM_PortName = ('/dev/ttyUSB0')
COM_Port = serial.Serial(COM_PortName) # open the COM port
print('\n ',COM_PortName,'Opened')
COM_Port.baudrate = 4800 # set Baud rate
COM_Port.bytesize = 8 # Number of data bits = 8
COM_Port.parity = 'N' # No parity
COM_Port.stopbits = 1 # Number of Stop bits = 1
COM_Port.setDTR(0) #DTR=0,~DTR=1 so DE = 1,Transmit mode enabled
COM_Port.setRTS(0) #RTS=0,~RTS=1 (In FT232 RTS and DTR pins are inverted)
#data = bytearray(b'\x02\x30\x33\x32\x33\x03\x33\x35') # Convert Character to byte array
SOF = b'\x02'
EOF = b'\x03'
SignAdd = b'\x30\x33'
MSG = input('\n Enter Number - ').encode()
ToCs=[SignAdd + MSG + EOF]
rc1 = gen(ToCs)
print("rc1=", rc1)
rc2 = "%x" % rc1
print("rc2=", rc2)
d1 = ord(rc2[0])
d2 = ord(rc2[1])
print("d =", d1, d2)
NoOfBytes = COM_Port.write(SOF) # Write data to serial port
NoOfBytes = COM_Port.write(SignAdd)
NoOfBytes = COM_Port.write(MSG)
NoOfBytes = COM_Port.write(rc2.encode())
print('\n message was - ',MSG)
COM_Port.close() # Close the Serial port
banner_bottom() # Display the bottom banner
dummy = input() # press any key to close and this is the erro I'm getting
Enter Number - 23
[b'0323\x03']
Traceback (most recent call last):
File "/home/pi/mu_code/MyProgram/RS485_Write.py", line 59, in <module>
rc1 = gen(ToCs)
File "/home/pi/mu_code/MyProgram/RS485_Write.py", line 23, in gen
lcs += b
TypeError: unsupported operand type(s) for +=: 'int' and 'bytes'maybe it will be easy if I read the number from a file?
I have a text file with "23" as it's content :
MSG = open('/home/pi/Documents/test.txt' , 'r') but now I get this error:
Traceback (most recent call last):
File "/home/pi/mu_code/MyProgram/RS485_Write.py", line 59, in <module>
ToCs=[SignAdd + MSG + EOF]
TypeError: can't concat bytes to _io.TextIOWrapper
Your output shows that p is a list with one element instead of a bytes instance. You neeed co call gen(ToCs[0])
yes , now it's working !
so what is the differant?
if ToCs have only 1 element , why do I need to tell the function to read just ToCs[0]?
Thanks
Quote:why do I need to tell the function to read just ToCs[0]?
This example explains the issue. Take the time to understand it
>>> p = [b'spam']
>>> for x in p:
... print(x)
...
b'spam'
>>> p = b'spam'
>>> for x in p:
... print(x)
...
115
112
97
109
>>>