# Serial port interface

<abstract>
A serial port interface at 3.3 volt is available on the CM-Home to connect external microcontrollers like Arduino or ESP8266. 
</abstract>

The signals are available on screw terminals as visible below and are at 3.3 volt level. 
<br>
<font color="red">These lines are not tolerant to 5 volt </font>.

<br/>
<img src="./cm3home_serial.jpg" class="img-responsive">

### Using the serial port

This port is visible in Linux as <code>/dev/ttyUSB3</code> device.

### Example in Python

Install the Python serial library:

	sudo apt-get update
	sudo apt-get install python3-serial 

This example sends a string on the serial port each 1 second at 115200,N,8,1 and checks
if any character is received from a remote serial terminal.

	#!/usr/bin/python
	import serial
	import time
	
	ser = serial.Serial(
	    port='/dev/ttyUSB3',
	    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".encode('utf-8') % (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".encode('utf-8') % (tx_counter,rx_counter,a,ord(a)))
	        print("Tx counter = %d | Rx counter = %d | Received: %s %02x" % (tx_counter,rx_counter,a,ord(a)))

### Listing ports

This command print the available serial ports. 

	$ python -m serial.tools.list_ports 
	
	/dev/ttyAMA0        
	/dev/ttyUSB0        
	/dev/ttyUSB1        
	/dev/ttyUSB2        
	/dev/ttyUSB3 

## Links

* [Python serial doc](http://pythonhosted.org/pyserial/)

<hr>

@include='adv_cmpanel'