Instead of directing the output to a file, the SOMOutCharRoutine procedure can be used to direct the output to a serial port. By connecting another computer or a dumb terminal to the serial port with a NULL modem cable, debugging information can be received on the remote terminal. A NULL modem cable is a specialized serial cable that has the transmit and receive wires crossed so that transmissions from one serial port are received by another.

First, initialize the serial port using the OS/2 Mode command. This command can be added to the STARTUP.CMD file or entered from an OS/2 command prompt. The following example shows how to use the Mode command:

MODE COM1 9600,n,8,1

Replace SOMOutCharRoutine with your procedure which directs somPrintf output to the COM1 serial port as shown in the following sample code:

#define INCL_DOS
#define INCL_WINWORKPLACE

#include <os2.h>
#include <io.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys\stat.h>
#include <string.h>
#include <som.h>

/* COM1 port for debugging information */
static FILE *DebugPort;

/**********************************************************************/
/*   This is the replacement for the default SOMOutCharRoutine.       */
/*   It writes the debugging information to the COM1 serial port      */
/*   instead of to stdout.                                            */
/**********************************************************************/

#pragma linkage(myCharacterOutputRoutine, system)

int SOMLINK myCharacterOutputRoutine(char chOut)
{
    fputc((int) chOut, DebugPort);
    fflush(DebugPort);

    return 1;   /* Indicate success */
}
   .
   .
   .

/**********************************************************************/
/*   Enable myCharacterOutputRoutine by opening the serial port       */
/*   and then changing the output character routine.                  */
/**********************************************************************/

DebugPort = fopen("COM1", "w");

fprintf(DebugPort, "\nDebug information from my WPS Object\n");
fprintf(DebugPort,   "------------------------------------\n");
setbuf(DebugPort, NULL);

SOM_TraceLevel  = 2;   /* Request maximum debugging information */
SOM_WarnLevel   = 2;
SOM_AssertLevel = 2;

/* All output goes to my routine after the next statement */

SOMOutCharRoutine = myCharacterOutputRoutine;