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Interrupt Routines

 
When an interrupt occurs, the event handler would typically perform the following steps: 1) find out what action needs to be taken, 2) perform the needed action, 3) perform whatever interface specific action is necessary to acknowledge the interrupt, and 4) re-enable interrupts with the ENABLE INTR command. The following example shows the typical sequence of statements used for interrupt set up and handling:
 
10   ON KBD CALL To_modem
20   ON INTR 9 CALL From_modem     !Tell BASIC to interrupt
30   ENABLE INTR 9;1               !Tell interface to interrupt
40   LOOP
50     DISP TIME$(TIMEDATE)        !Now free to do something
60   END LOOP                      !while you wait
70   END
80   SUB From_modem
90     WHILE BINAND(STATUS(9,10),1)
100      PRINT CHR$(STATUS(9,6));  !Interface dependent ack.
110    END WHILE
120    ENABLE INTR 9;1             !re-enable the interrupt
130  SUBEND
140  SUB To_modem
150    OUTPUT 9;KBD$;
160  SUBEND