Asynchronous SeaTalk

Hope I've posted in the right place.
Last Monday somebody told me about the Arduino.  By the w.end  had a Relay shield driving motors in response to switches.  Now I'm loosing what hair I have left.

Big project, build a modular control system for a 40' sailing yacht (so that a high level quadriplegic can sail it).
Current step, replicate the PIC based system that controls her existing 20' boat (hence switches and motors).  Built by a guy in Canada some years ago, don't have very much info.
Current problem, getting a Mega to talk to a Raymarine ST4000+ autopilot.

The ST4000+ talks to the world over SeaTalk (see http://www.thomasknauf.de/seatalk.htm).  SeaTalk is a Raymarine proprietary bus. 
11 bits are transmitted for each character:
  1  Start bit (0V)
  8  Data Bits
  1  Command bit
  1  Stop bit (+12V)

Where I am at the moment is reading SeaTalk on Serial 3 and then sending it to Serial Monitor over the USB.  It looks like rubbish. What I want to know is how to set the serial port to 11 bits?  Is there a command or procedure?   How much control can be had over how the serial ports work?

In the Thomas Knauf article there code in C with the line:

_outb(0x3B, PORT+3); /*LCR Stick Parity to 0, Enable Parity, 1 Stop bit, 8 bits/char */

Does Arduino C++ have an equivalent command?

Thanks

Toby

Kristina

Err...yes, the ST4000+ has NMEA0183. 

Getting the SeaTalk working on this is a stepping stone to getting access to another set up (S1 tiller pilot, C80, ST60 instruments) on another boat.  I want to be able to access the SeaTalk bus, read messages and send messages.  I eventually want to be able to plug any manufacturers equipment into a boat control computer.  Got to start somewhere.

So, how do I set up the serial port?

Toby

Nick

Code is below.

Data sheet I have (2549M-AVR-09/10), "8-Bit AVR Microcontroller with...." is talking about PWM on page 180, so I guess its not the one you are talking about.  Page 215/216 looks like what your talking about but I don't have a clue how to write this into a sketch.


/*
  HLOR / Toby May
  Experimental stuff with Arduino Mega and home made hardware interface to SeaTalk.
  Rx only. 
  I.Face is a pair of resistors as a voltage dropper.
  Receives on serial port 3, sends to the main serial (Serial 0) and then to Monitor on a laptop.
  This example for Arduino Mega
  WORK IN PROGRESS - may not work!!!!!
*/

char not_receiver_buf,receiver_buf;

void setup()                                        // initialise both serial ports
  {
    Serial.begin(9600);   
    Serial3.begin(4800);
  }

void loop()
  {                                                 // Continuous data processing loop 
  if((Serial3.available()) > 0)                     // LSR New SeaTalk Data received ?
     {
        receiver_buf=Serial3.read();                // RBR Read SeaTalk Data Byte
        not_receiver_buf=~receiver_buf;             // Invert received character...
        Serial.println(not_receiver_buf, HEX);      // ...and prints it out. 
     }
  }

In the Thomas Knauf article there code in C with the line:

_outb(0x3B, PORT+3); /*LCR Stick Parity to 0, Enable Parity, 1 Stop bit, 8 bits/char */

By the way, this is doing it a different way. I am guessing he is using space parity, which means "the parity bit is always zero". There is also mark parity which is "the parity bit is always one". However browsing the Atmega documentation it doesn't seem to support mark and space parity (only odd, even and none).

If your device supports space and mark parity, then that is a way (perhaps a rather obscure one) of putting a 0 or 1 into the 9th bit.

Yes indeed. Looking at the datasheet is always interesting. It is interesting that they allow for 9 bits OR parity. It's almost as if the 9th bit is "parity on the fly".

Anyway, this seemed to work for me, to change the 9th bit for every other byte:

void loop()
  {                                         
  Serial.print ("a");
  UCSR0B = 0b10011101;  // turn 9th bit on
  Serial.print ("a");
  UCSR0B = 0b10011100;  // turn 9th bit off
  }


The low-order bit of the UCSRnC register (where n is the serial port) is the 9th bit. So by setting or clearing that before you send a byte, you control the contents of the 9th bit.

teeman,
could you share your softwareserial mod?  I have Thomas Knauf's code for a pc, but bridging the gap in my understanding of how to mod the usart on the arduino uno is still beyond me.

best, john

David,
Frank Wallenwein makes an excellent nmea-seatalk bridge.  It is an ATMEGA32 small computer which accepts seatalk and nmea sentences and converts each type to the other and sends them out to their respective ports.  I have one and it works brilliantly allowing me to show depth, windspeed and windangle on my notebook computer running PolarView (an inexpensive and excellent charting program which runs on Linux, MacOS, and Windows).

you get all of Frank's code on a cd when you buy the bridge (something about buying a bridge seems a bit off, but there it is).  Code is C and wrritten for the Atmega32 .

my effort is to get part of it ported to arduino uno, although I think I'm going to get a mega2560 - won't have to cut so much.  i wanted a repeater in my berth which shows heading, windspeed, wind-direction, depth, and distance and bearing to last time I pressed rest button - for drag detection.

I can do all this by feeding nmea-seatalk bridge data to arduino and input from arduino mounted tilt compensated compass, but I thought it would be better just to feed seatalk to arduino (wind and depth) and have one fewer devices running.

you may be able to get Frank's code if you ask him - don;t know, but i thought the Bridge was well worth the price.

he's at:

http://www.gadgetpool.de/nuke/modules.php?name=Forums&file=viewforum&f=12

As I mentioned further up, you can do the 9th bit with hardware serial. Can't you rejig your design so you use hardware serial for the 9-bit comms?