Raspberry PI writing to RS485 driver, DIR pin not holding state

[zazas321]

Hello. I am writing data to my modbus DRIVER and learning about modbus in general. I am using logic analyzer to check my signals.

I have noticed a very strange behaviour of my DIR pin. Before I send data to RS485 driver, I toggle DIR pin HIGH and keep it HIGH until the data transfer is finished.
The code:

# \x02 - trigger scanning
# \x03 after scanning is done
import serial
import RPi.GPIO as GPIO
import time
sendSerial = serial.Serial ("/dev/serial0", 9600)
GPIO.setmode(GPIO.BOARD) # Use physical pin numbering
GPIO.setup(16, GPIO.OUT) # Set pin 10 to be an input pie to be pulled low (off)

GPIO.output(16,1)
sendSerial.write (str.encode("hello"))
GPIO.output(16,0)

print("done")


sendSerial.close()

And the signal analzyer shows:
https://ibb.co/xsJR28b

As you can see from the image above, the DIR pin does not want for the serial write to finish

I have tried to add :
sendSerial.flush() after the writing but it looks even more strange:
https://ibb.co/qy0CDXv

Now its holding DIR pin for way too long.

Can someone help me understand this strange behaviour and how to fix it?

[deanhystad]

Serial I/O is buffered. You usually don't want to wait for the write to complete. I was looking at the PySerial documentation and it looks like you could loop until out_waiting is zero if waiting until done is important.

[zazas321]

Serial I/O is buffered. You usually don't want to wait for the write to complete. I was looking at the PySerial documentation and it looks like you could loop until out_waiting is zero if waiting until done is important.

Its not that I want to wait. The rs485 driver requires me to hold the DIR pin high untill all bytes are transmittet.But as you can see from the examples of code I have posted above , the program wont let me do it. How can i build a proper modbus structure then?

From what I undestood, the serial.flush() function should do the job but it does not