This "FPGA" is also known for a security measure named "antifuse". There are readable contents but they are all encrypted.
An oscillator and DS1232, microchip monitor, are present on this pcb meaning there has to be some sort of custom MCU well hidden inside that A42MX09. Very clever to use a protection device/MCU to control inputs.
Some Sega Naomi carts also used a different "antifuse" Actel FPGA for encryption which is understood. Someone, possibly MetalliC, should explain how this Actel FPGA functions to get a better understanding to hook Area 51 Site 4's inputs.
A basic understanding on Actel's antifuse protection scheme: https://www.microsemi.com/document-porta...device-security
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