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

Unidirectional SeaTalk => RS232 Interface

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 */
       buffer[in_ptr++]='\n';
       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

SeaSigma: A simple SeaTalk command generator

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