USR Function - Plus/4 Encyclopedia



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USR Function
Category Reference/Commodore BASIC V3.5 Topic USR(X) This function returns a numeric value. When this function is called, a machine language routine is executed at the memory location specified at location 1281-1282 ($0501-$0502, low byte-high byte format). The location of the routine must be entered with the POKE statement into locations 1281-1282. If no values have been entered, calling the USR function will cause an ?ILLEGAL QUANTITY ERROR. When the USR function is called, the value of X is placed into floating point accumulator #1 ($61-$66). When an RTS instruction (outside of a JSR subroutine) is executed, program execution returns to BASIC and the value in floating point accumulator #1 is returned by the USR function. For immediate execution of a machine language program from BASIC, use the SYS statement. Abbreviation U SHIFT+S