Two things are required: first we have to set up a bit of assembler to do the equivalent of the VDU 23 command, by calling OSWRCH, the bit of the operating system which sends the contents of the Accumulator to the VDU drivers, and secondly we have to change the BREAK vector to point to the bit of code so that it is executed every time the BREAK key is pressed.

I've assembled the code at &900 (which is all very well although the Tube must be off when it's run otherwise the BASIC, which starts at &800 in the Tube RAM, will be overwritten with the machine code) and the the three OSBYTE calls at the end put an opcode 76, which is JSR, followed by the location &900 into the BREAK vector.

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