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Information in this article applies to:

  • RTX51 Version 5.10b


How do I create an interrupt service routine in RTX51?


Using interrupt service routines in RTX51 is pretty straight-forward.

  1. Create the interrupt service routine as you would in a standard Keil C51 program. This is the int0 function in the following example.
  2. Create some code that enables the interrupt source. The statements EX0 = 1; and IT0 = 1; in the startup task do this.
  3. Call the os_enable_isr function and pass the interrupt number. This is also done in the startup task.

For example:

#include <rtx51.h>
#include <reg51.h>
#include <stdio.h>

#define STARTUP_TASK 0

void int0 (void) interrupt 0
static unsigned int i;


void task0 (void) _task_ STARTUP_TASK
os_set_slice (1000);        /* Set for OSC Frequency / 10,000 */

EX0 = 1;                    /* Enable External Int 0 */
IT0 = 1;                    /* Edge-triggered */

os_enable_isr (0);          /* Enable interrupt #0 */

while (1)
  os_wait (K_TMO, 100, NULL);
void main (void)
os_start_system (STARTUP_TASK);


You may download this complete RTX51 example for µVision from the Keil website.

Last Reviewed: Thursday, September 22, 2005

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