Does anyone know if the above is identical in spec to the "official" Zilog PIO chip? The manual's dated November 1976 and stamped as preliminary, which is a little unsettling :) I want to do some messing around with a Z80 CPU and PIO, and having a physical paper reference to hand would sure be useful - I'm just not sure if I'm going to shoot myself in the foot using this particular one! I should go and google for Zilog / Z80 history I suppose to see where Mostek fit into things - I've got a rather thick Mostek UK Z80 programming manual (V2.0) too which would also make a useful reference, assuming it's sound for all Z80 chips regardless of source... cheers Jules