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Z80 system, with EPROM, RAM, 8255 PIO

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Some EPROMs require 0 or +5 at the VPP pin to enable read, on most 27C256 tire VPP to +5
The EXO-3 is some sort of an Xtal? Oscillator with selectable divider
The PST520A is a low-voltage controlled reset

Memory map:
EPROM = 0000h - 7fffh
RAM   = 8000h - ffffh 

IO map:
Base adr. PIO 1 = 40h
Base adr. PIO 2 = 80h