CRCs and Serial Ports

Scope

This mini guide explains how to append messages with CRCs and send them to a serial port.  Operating a serial port from the Linux Bash shell is very obscure and precious few people know how to do it.

Once you know the tricks, it is extremely powerful and a big time saver over the more complicated and error prone alternatives.

Also see this: http://www.aeronetworks.ca/2014/07/fletcher-checksum-calculator-in-bash.html

Get a set of CRC utilities from here:

http://www.hampa.ch/misc-utils/index.html

http://www.hampa.ch/misc-utils/misc-utils-0.2.2.tar.gz

Install the tools:

$ cd

$ mkdir misc

$ cd misc

$ wget http://www.hampa.ch/misc-utils/misc-utils-0.2.2.tar.gz

$ tar -zxvf misc-utils-0.2.2.tar.gz

$ ./configure

$ make

$ su

password

# make install

CRC Message Preparation:

Prepare a message step by step:

$ echo -en "\xa5\x10\x01\xca" > msg

$ hex msg

A5 10 01 CA # 00000000  ....

$ crc -g crc16 msg

41cf

Or modify the message file on the fly:

$ crc -b -g crc16 msg >> msg

$ hex msg

A5 10 01 CA 41 CF # 00000000  ....A.

Or do it all in one line:

$  echo -en "\xa5\x10\x01\xca" | crc -b -g crc16 - >> msg

Serial Port Tricks

Set the serial port in raw mode and configure it:

# stty -F /dev/ttyUSB0 raw

# stty -F /dev/ttyUSB0 19200

Prepare a message with a CRC16 and send it straight to the serial port:

$  echo -en "\xa5\x10\x01\xca" | crc -b -g crc16 - >> /dev/ttyUSB0

Serial Port Tips

www.aeronetworks.ca/2015/01/serial-port-io.html
www.aeronetworks.ca/2014/10/serial-ports-revisited.html
www.aeronetworks.ca/2014/01/crcs-and-serial-ports.html
www.aeronetworks.ca/2013/10/serial-port-tricks.html
www.aeronetworks.ca/2013/05/usb-serial-device-with-unknown-ids.html
www.aeronetworks.ca/2015/10/reading-and-parsing-data-from-serial.html
www.aeronetworks.ca/2013/05/compile-moxa-serial-widget-device.html

La voila!

Herman