Navigation: Home =>Profil=>SeaTalk=>Part3
Stand: 01.09.2003

SeaTalk Technical Reference Part 3: Processing SeaTalk Data with a PC

Unidirectional SeaTalk => RS232 Interface

This simple unidirectional interface circuit inverts the SeaTalk signal to make it readable by the PC serial port:

Bidirectional SeaTalk <=> RS232 Interface

For bidirectional communication the circuit has to be extended by a second transistor:

A PC-board may be obtained from Frank Wallenwein.

SeaTalk Monitor

The following piece of C-code gives an example of how to collect and process SeaTalk data. It monitors the SeaTalk bus and echoes the SeaTalk datagrams in hexadecimal notation to the screen.

#include <stdio.h>

/* Set Address of Serial Port: COM1=0x3F8, COM2=0x2F8 */
#define PORT 0x3F8

unsigned int collision_ctr,overrun_ctr;
char buffer[256],in_ptr,out_ptr,limit_ptr;
char line_status_reg,receiver_buf,byte_ctr;
char hex[]="0123456789ABCDEF";

main() {
  puts("SeaTalk Monitor Rev. 1.01    (c)2000 by Thomas Knauf\r\n");

 /* Serial Port Initialization */
 _outb(   0, PORT+1); /*IER Disable Interrupts */
 _outb(   1, PORT+2); /*FCR Enable Fifo */
 _outb(0x80, PORT+3); /*LCR Enable access to Divisor Latch */
 _outb(  24, PORT  ); /*DLL Set Baud Rate to 4800 LSB*/
 _outb(   0, PORT+1); /*DLM Baud Rate Divisor MSB */
 _outb(0x3B, PORT+3); /*LCR Stick Parity to 0, Enable Parity, 1 Stop bit, 8 bits/char */
 _outb(0x0F, PORT+4); /*MCR Disable LOOP Mode */
 _outb(   0, PORT+5); /*LSR Clear Error flags */

 while(1) { /* Continous data processing loop */
   if((line_status_reg= _inb(PORT+5)) & 1) { /* LSR New SeaTalk Data received ? */
     receiver_buf=_inb(PORT);  /* RBR Read SeaTalk Data Byte */
     if(line_status_reg & 2) overrun_ctr++; /* PC too slow, should not happen */
     if(line_status_reg & 4) { /* Parity bit set => Command Byte */
       if(byte_ctr) {         /* More characters expected => Collision */
         in_ptr=limit_ptr;    /* Discard last datagram, restart from beginning */
         collision_ctr++;     /* Count collision events */
       buffer[in_ptr++]='\r';  /* Put new command on new line */
       byte_ctr=255;           /* Undefined datagram length, wait for next character */
     } else
       if(byte_ctr==254)       /* Attribute byte ? */
         byte_ctr=(receiver_buf & 0xF) + 2; /* Read expected datagram length */
     if(byte_ctr) {            /* Process valid data bytes, should always be true */
       buffer[in_ptr++]=hex[receiver_buf >>  4]; /* Convert Data to hex */
       buffer[in_ptr++]=hex[receiver_buf & 0xF];
       buffer[in_ptr++]=' ';                     /* Seperate by space */
       if(! --byte_ctr) limit_ptr=in_ptr;        /* Complete datagram ready for output */
   } else
     if(out_ptr != limit_ptr)          /* Characters waiting for Output ? */
       putc(buffer[out_ptr++],stdout); /* Copy single character from buffer to screen */
     else if(scr_csts()) break;        /* Query keyboard, terminate if any key hit */
 printf("\r\nSeatalk Collisions : %5u",collision_ctr);
 printf("\r\nUART Overrun Errors: %5u",overrun_ctr);

Compiled EXE-Files can be downloaded here as SEAMON1.EXE (using COM1:) or SEAMON2.EXE (using COM2:). They run in any MS-DOS environment. Redirecting the output logs data to a file (example: SEAMON1 > LOGFILE). Pressing any key terminates the program.

SeaTrack: Route documentation software

The SeaTrack software developed by Philip Beekman for reading editing combining displaying and saving trip routes is able to handle SeaTalk data directly. The author also describes how he solved the problem to handle the parity/command-bit interpetation within VisualBasic.

SeaSigma: A simple SeaTalk command generator

The file contains a MS-Windows program which allows to generate SeaTalk commands and to send them via COM1: or COM2: to the SeaTalk bus. Since SeaSigma is a contribution of Ales Janhar I cannot give support or take any responsibility for this software.

Return to Top of Page   Overview   Part 1     Part 2