Not all software routines are compatible with the TUBE (e.g. the 6502 co-processor) in use so being able to check for this can be handy.

The code below will test for the TUBE and if detected notify the user and end the program. If the TUBE is not detected then the program will branch to the label 'routine' where your own code can go.

  10 DIM mc% 100

  20 osasci=&FFE3

  30 osbyte=&FFF4

  40 FOR opt%=0 TO 2 STEP 2

  50 P%=mc%

  60[          OPT opt%

  70           LDA #&EA

  80           LDX #&00

  90           LDY #&FF

 100           JSR osbyte

 110           CPX #&00

 120           BEQ routine

 130           LDY #&00

 140.loop      LDA message,Y

 150           JSR osasci

 160           INY

 170           CMP #&0D

 180           BNE loop

 190           RTS

 200.message   EQUS "TUBE detected!"

 210           EQUB &0D

 220.routine   \ rest of program here

 230           RTS

 240]

 250 NEXT

 260 CALL mc%

The proper way is to detect which side of the Tube you are executing on. If you're executing in the I/O processor it's irrelavant whether there's a Tube active or not.

 LDA #130:JSR OSBYTE   :\ Read address high word

 INX:BNE LangProcessor :\ Not &xxFF

 INY:BNE LangProcessor :\ Not &FFxx

 \ &FFFFxxxx, executing in I/O processor