PySerial Works in a different way with USB to rs232 and MAX3232CDR

Asked Jul 23 '17 at 07:42

Active Jul 23 '17 at 08:53

Viewed 91 times

Can anyone explain where my mistake is

import time, serial
from _poll_msg import *
from exception import BadCRC
ser = serial.Serial()
ser.parity = serial.PARITY_NONE
ser.baudrate= 19200
ser.port = '/dev/ttyUSB0'
ser.open()

def write(cmd):
    ser.flushOutput()
    ser.parity = serial.PARITY_MARK
    ser.write(('82'+ mashin_n).decode('hex'))
    crc = crc_sas(mashin_n + cmd)
    cmd = cmd + crc
    ser.parity = serial.PARITY_SPACE
    ser.write(cmd.decode('hex'))
    return True

def read(size):
    response = ser.read(size).encode('hex')
    # with ttyUSB? response is 011912345678crc
    # with ttyS? response = 0101010101
    # but error is in write (010101 - command is bad)
    time.sleep(0.2)
    try:
        crc_sas(response, chk=True)
    except BadCRC:
        return False
    return response[4:-4]

It works without error. But if I change port to /dev/ttyS1 It does not work. Where's the difference and where I'm wrong.

edited Jul 23 '17 at 08:53

asked Jul 23 '17 at 07:42

Grigor Kolev

Exception is BadCRC. From doc response is: mashin_n, cmd, 4 bit bcd, 2 bit crc (011912345678crc) If port is /dev/ttyS? It return 010101010101 (comand is bad) – Grigor Kolev Jul 23 '17 at 08:39
No python traceback just machin not recognize command. – Grigor Kolev Jul 23 '17 at 08:55
Oh, you are messing about with parity in the write function. Oh, go figure. – barny Jul 23 '17 at 09:02
Communication is 9 bit Parity makes that. With USB it work. Function write and read 24 h 7 day on every 0.5 s and their 3 bad crc exception – Grigor Kolev Jul 23 '17 at 12:43

PySerial Works in a different way with USB to rs232 and MAX3232CDR

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