Hello,

For most of the machine control applications that I code, I normally have a I/O count exceeding the ones directly available on the MCU and hence resort to memory mapped I/O with all peripherals mapped from 0xF000 onwards .
For inputs I use a 74138 to select one from the 8 busdrivers 74244 to which inputs are connected - thus I can get 64 inputs.

Similiarly for outputs I use 74138 +7400 for inverting the Enable + 74374 and I get 64 outputs maximum.

As such the present requirement of 56 I/O also can be handled.

But I want to know if there are any other elegant ways to handle the above job with lesser numbers of chips. ( The above arrangement needs about 26 Chips )For commercial / compatibility reasons I have to use only 89c51rd2.

Thanks

Raghu