Assembly-language subroutines
Mike Costello · 1983
This chapter provides two kinds of subroutines for a ZX81 Assembly Language programmer. The first kind uses the ROM calls described in the previous Chapter and shows how they can be applied safely. The second type comprises general-purpose subroutines which are likely to be needed by any programmer doing work in Z80 Assembler, and will save him time which might otherwise be spent reinventing the wheel. Some of the routines are quite short and may tempt the BASIC programmer into learning Assembler in order to make his ZX81 a more powerful machine, which in effect is what Assembler has to offer him. However, to repeat the point made earlier, this book does not teach Assembler from scratch although the routines may be found worth studying as examples of applications techniques on the ZX81.