modbusmaster/readme.md

# modbusmaster

## Disable Bluetooth on RPi3

Add at the end of `/boot/config`:

    dtoverlay=pi3-disable-bt

Remove mentions of `serial0` from `/boot/cmdline`.


## Enable rs485 mode

Use the submodule rpirtscts to enable to alternate functions of the related
pins at the RPi MCU. It is submoduled here, can be found directly at https://github.com/mholling/rpirtscts

    cd rpirtscts
    gcc -o rpirtscts rpirtscts.c
    sudo ./rpirtscts on

This needs to be done at every boot.

Kudos to danjperron, cmp. https://www.raspberrypi.org/forums/viewtopic.php?f=98&t=224533&hilit=rs+485#p1383709

(Note, please: This software is under the GPL 3.0 license. However, I do not derive from this software, I use it in an unchanged way. It is not integrated into my sources, it just needs to be called once the RPi has booted.)

## Pinout

Find a good pinout diagram at https://raw.githubusercontent.com/ppelleti/hs-wiringPi/master/pin-diagram.png.

TX is at GPIO14, RX is at GPIO15 and RTS (control line for transmitter enable) is at GPIO17.


## Schematics

![Schematics](./docs/IMG_1860.jpeg)


## Python snippet to test

(See also `./snippets/test1.py`.)

    import serial.rs485
    ser=serial.rs485.RS485(port='/dev/ttyAMA0',baudrate=2400)
    ser.rs485_mode = serial.rs485.RS485Settings(False,True)
    ser.write('a test'.encode('utf-8'))

Find an signal screenshot here:

![Test1 Signals](./docs/osci1.png)

Channel 1 in yellow has the TX line (GPIO14), channel 3 in purple has the RTS (GPIO17, transmitter enable line).