CODEWITHSUNDEEP
python-3.xserial-port
Willy Wonka
Willy Wonka

Reputation: 148

Cannot send (Or do not receive) a 0 value in serial Python

I have connected my RPi3 Tx and Rx pins together. I use the following code:

import serial
from time import sleep

ser = serial.Serial(
        port='/dev/ttyS0',
        baudrate = 9600,
        parity=serial.PARITY_NONE,
        stopbits=serial.STOPBITS_ONE,
        bytesize=serial.EIGHTBITS,
        timeout=10
)
while True:
    
    ser.write(0)
    sleep(1)
    incoming = ser.read(ser.inWaiting())
    print(incoming)

This prints empty b''. I can do this: '0'.encode() and then I get b'0'. I need to send packets of data to a sensor: bytearray({0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}). The issue is that in loopback I get incomplete package, and it is out of order. It seems that after the first '0' that gets sent it terminates, or something else happens. What is the correct way to send commands like this? I also tried ser.read(9) since I expect 9 bytes, but it still cuts it off.

Upvotes: 1

Views: 674

Answers (1)

meuh
meuh

Reputation: 12255

The problem lies with

bytearray({0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79})

where the {...,} syntax is being used to construct a set. This is an unordered list of unique items. Hence the multiple zero bytes become just one, and the order is arbitrary. Instead, use a list:

data = bytearray((0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79))
ser.write(data)

Upvotes: 1

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