CM3-Home technical documentation Buy
RS-485 interface
The RS485 is commonly used to connect DMX512, Modbus or generic RS485 serial devices.
What is a RS485 ? What is a DMX512 ? What is a Modbus ?
Two RS485 lines are available on CM3-Home model Full and one on the model Basic. The lines are opto-isolated from the CPU and available on screw terminals as shown below.
How to use the RS485 ports
The ports are visible by Linux on /dev/ttyUSB0 (left port) and /dev/ttyUSB2 (right port) and can be managed by software like any other serial line. The DE signals required to get the bus are managed by the hardware on FTDI FT4232 chip.
Python example
Send and receive chars on the right RS485 port. To do the same on the left port change /dev/ttyUSB2 with /dev/ttyUSB0.
#!/usr/bin/python
import serial
import time
ser = serial.Serial(
port='/dev/ttyUSB2',
baudrate=115200,
timeout=1,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS
)
ser.flushOutput()
ser.flushInput()
rx_counter=0
tx_counter=0
while True:
tx_counter=tx_counter+1
ser.write("Tx counter = %d | Rx counter = %d\n\r" % (tx_counter,rx_counter))
print("Tx counter = %d | Rx counter = %d" % (tx_counter,rx_counter))
a=ser.read(1)
if a:
rx_counter=rx_counter+1
ser.write("Tx counter = %d | Rx counter = %d | Received: %s %02x\n\r" % (tx_counter,rx_counter,a,ord(a)))
print("Tx counter = %d | Rx counter = %d | Received: %s %02x" % (tx_counter,rx_counter,a,ord(a)))
