Call a machine code subroutine

Requires: 6502 assembler

The machine-code routine must end in RTS and can return a 16bit value in the A- and Y register. If the A- and Y-Register are not set, the return value "res" has a random value and should not be used.

\NEEDS CODE   INCLUDE" D:TAS65.F"

( Call Machine Routine at "addr" )
( return value is A-Reg and Y-Reg)
HEX
 CODE CALL ( addr -- res )
   4C # lda   n sta
   SP x) lda  n 1+ sta
   SP )y lda  n 2+ sta
   n jsr
   n sta
   n 1+ sty
   00 # ldx
   01 # ldy
   n    lda  SP x) sta
   n 1+ lda  SP )y sta
   next jmp end-code