those are instructions for an extended Z80 processor, i think the Z180. mlt hl, for example, does hl=hl*hl. we don't have to worry about them because so far TI hasn't used a Z180 in a calc. Kirk Dux Gregis wrote: > What do some of these instructions do? > > ino a,(x) > mlt hl > otdmr > outo (x),a > tst (hl) > > Thanks.