Echo = $FFEF
Monitor = $FF1F

LDX #$00          ;  Our loop expects X to start at 0

print:
  LDA string,X    ;  Load the next character
  CMP #$00        ;  Compare char to NULL ($00)
  BEQ done        ;  If NULL break out of loop
  JSR Echo        ;  If not NULL, print the character
  INX             ;  Increment X, so we can get at the next character
  JMP print       ;  Loop again

done:
  JMP Monitor     ;  Return to Monitor
  
string:
  .asc "HELLO WORLD",$00    ;  ASCII string, $00 is NULL

