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SBASIC Manual - Page 45

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     SBasic User's Manual     SBasic Version 2.7             Page 45
     Printed:  December 5, 1999

     SBasic provides support for processing interrupts on the target

     You can write interrupt service routines (ISRs) directly in SBasic,
     rather than having to drop down into assembly language for the target
     machine.  However, you must declare a block of SBasic code as an ISR
     by using the INTERRUPT statement.

     The INTERRUPT statement can accept a single argument, which is the
     address on the target system to use as an interrupt vector.  SBasic
     will determine the address of the ISR code, then write that address to
     the vector address you specify.

     Later, when your program is running on the target system, an interrupt
     will cause control to transfer to the address stored in the vector
     address.  This in turn starts execution of your SBasic routine.


          interrupt $fff0          ' use $fff0 as the interrupt vector
          a = peekb(porta)         ' read 8 bits from port A
          end                      ' return from the interrupt

     Given the above example, an interrupt that uses $fff0 as its vector
     will cause control to jump to the statement containing the PEEKB
     function.  This small program will read a value from port A, then
     return from the interrupt.

     Note that your SBasic routine does not get written to address $fff0;
     only the address of your routine gets written there.  If necessary,
     examine the code created by the compiler to help understand how SBasic
     interrupts work.

     You must use an END statment to terminate all ISR code following an
     INTERRUPT statement.  When it processes this END statement, SBasic
     compiles the proper Return from Interrupt instruction for the target

     You sometimes need more than one exit from an ISR.  If so, simply use
     the RETURN statement to exit the ISR.  SBasic will automatically
     compile the proper instruction for leaving the interrupt section.


          interrupt $fff0
          if n = $66
          n = $10