glitch
Veteran Member
Don't forget that the 8085 also mirrors the 8-bit I/O address in the upper address byte. That makes expansion really easy, as you do not need to demultiplex the address and data buses to obtain an I/O address. The simplest latched input or output port could be constructed with a 74LS373 latch, a 74LS688 comparator, one inverter/NOT gate, and an 8-position DIP switch. Qualify the 74LS688 by inverting the IO//M line and feeding it into the 74LS688's /E pin, and tie the /LE pin of the 74LS373 to the /RD or /WR line, depending on if you want an input or output port. For the board real estate, you might be better off with a 8255 PIA (or the 8085 bus-specific 8155).