Frequently Asked Questions

Using Multiple RS-232 Ports on a PIC^® MCU or PIC^® DSC

In order to use multiple RS-232 connections on a PIC^® MCU or PIC^® DSC, multiple #USE RS232 pre-processor directives will need to be setup using the STREAM option. A #USE RS232 pre-processor directive will remain in effect for GETC, PUTC, PRINTF and KBHIT functions until another #USE RS232 is encountered.

The following example program shows how to read from one RS-232 port (A) and echo the data to both the first RS-232 port (A) and a second RS-232 port (B) without using the STREAM option for #USE RS232:

#USE RS232 (BAUD = 9600, XMIT = PIN_B0, RCV = PIN_B1)

void put_to_a(char c) {
   put(c);
}

char get_from_a(void) {
   return(getc());
}

#USE RS232 (BAUD = 9600, XMIT = PIN_B2, RCV = PIN_B3)

void put_to_b(char b) {
   putc(c);
}

void main(void) {
   char c;
   
   put_to_a("Online\n\r");
   put_to_b("Online\n\r");
   
   while(TRUE) {
      c = get_from_a();
      
      put_to_b(c);
      put_to_a(c);
   }
}

The following example program will perform the same operations as the one above. The STREAM option in the #USE RS232 pre-processor directive makes the code more readable and is therefore recommended method:

#USE RS232 (BAUD = 9600, XMIT = PIN_B0, RCV = PIN_B1, STREAM = COM_A)
#USE RS232 (BAUD = 9600, XMIT = PIN_B2, RCV = PIN_B3, STREAM = COM_B)

void main(void) {
   char c;
   
   fprintf(COM_A, "Online\n\r");
   fprintf(COM_B, "Online\n\r");
   
   while(TRUE) {
      c = fgetc(COM_A);
      
      fputc(c, COM_A);
      fputc(c, COM_B);
   }
}

For more information or additional help about using multiple RS-232 ports on a PIC^® MCU or PIC^® DSC, contact CCS Technical Support.