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       INTERRUPT SERVICE ROUTINE CONTROL (ISROFF and ISRON)
       ----------------------------------------------------------------
       ISR (Interrupt Service Routine) like MOUSE or Screen dumps or any
       special program like XB Packer use a ISR. The problem with these
       programs is unless they are written to work with new devices, a
       lock-up occurs. EXAMPLE: running a mouse routine and XB Packer.
       They were never made to work together. RXB now has a handle on
       this. CALL ISROFF turns off the interrupt and saves the address
       for turning it back on. CALL ISRON restarts the interrupt. As
       several pages of the AMS can be used with interrupts a whole
       new world of programming is now possible.
       NO ASSEMBLY IS USED OR CALL LINKs. Absolute compatibility.
 
       4K PROGRAM IMAGE FILE LOADER AND SAVER (PLOAD and PSAVE)
       ----------------------------------------------------------------
       Hidden loaders were created to overcome the slow loading speed
       of CALL LOAD. The disadvantage of a hidden loader is it can only
       load one assembly support program at a time. PLOAD loads program
       image files of 4K, and PLOAD can load as many times as needed
       within one RXB program. PSAVE is the opposite and creates the 
       program image files of the 4K anywhere in memory. Lastly loading
       200K into the SAMS card is easy with PLOAD. A simple loop can 
       load each SAMS 4K page with PLOAD. Each address boundry is in
       PSAVE or PLOAD like SAMS uses boundry symbols upper case only.
       i.e. 2 = >2000, 3 = >3000, A = >A000, B = >B000, C = >C000,
       D = >D000, E = >E000 and F = >F000 
      
       SAVE FILES IN INTERNAL VARIABLE 254 OR PROGRAM IMAGE FORMAT
       ----------------------------------------------------------------
       RXB allows XB programs to load or be saved in two formats as
       previously, but now RXB allows more control of this feature.
       Normally XB will save files in Program Image format if these
       programs are small enough to fit in VDP memory. If these XB
       programs are larger then what will fit in VDP then XB programs
       will be saved in Internal Variable 254 format. RXB has a added
       feature added to save command. IV254 is the new feature. 
       EXAMPLE: SAVE DSK3.TEST,IV254