The analog inputs are read from memory mapped ASIC registers:
6808h ADC0 Analogue Joystick 1, X-Axis (00h=Left= [maybe 0 ohm???], 3Fh=Right= [maybe 1xx Kohm???]180K ohm) 6809h ADC1 Analogue Joystick 1, Y-Axis (00h=Up = [maybe 0 ohm???], 3Fh=Down = [maybe 1xx Kohm???]180K ohm) 680Ah ADC2 --unknown: MIGHT be Analogue Joystick 2, X-Axis (or Y-Axis00h=Left=0 ohm, or whatever3Fh=Right=180K ohm) 680Bh ADC3 --unknown: MIGHT be Analogue Joystick 2, Y-Axis (or X-Axis00h=Up =0 ohm, or whatever3Fh=Down =180K ohm) 680Ch ADC4 --unknown: MIGHT be unused (maybe Unused, wired to GND or VCC+5V (twice the maximum of 2.5V) (returns 3Fh) 680Dh ADC5 --unknown: MIGHT be unused (maybe Unused, wired to GND or VCC(equivalent to 0 ohm) (returns 00h) 680Eh ADC6 --unknown: MIGHT be unused (maybe Unused, wired to GND or VCC+5V (twice the maximum of 2.5V) (returns 3Fh) 680Fh ADC7 --unknown: MIGHT be unused (maybe Unused, wired to GND or VCC(equivalent to 0 ohm) (returns 00h)
To read that registers: Unlock the ASIC, and then map its register to memory at 4000h..7FFFh.