Master System

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The Sega Master System, released in 1986, is a third-generation home video game console manufactured by Sega.

Technical Specifications

Region Detect

The region detection code used in Master Games attempts to write to the two most significant bits in I/O port $3F and to read back the value at I/O port $DD. Japanese systems will not readback the write value at $DD, overseas systems will.

;==============================================================
; Region detector
; Returns a=1 for Japanese, 0 for export
; Based on code found in many Sega games (eg. Super Tennis)
;==============================================================
IsJapanese:
    ld a,%11110101  ; Output 1s on both TH lines
    out ($3f),a
    in a,($dd)
    and %11000000  ; See what the TH inputs are
    cp %11000000  ; If the input does not match the output then it's a Japanese system
    jp nz,_IsJap

    ld a,%01010101  ; Output 0s on both TH lines
    out ($3f),a
    in a,($dd)
    and %11000000  ; See what the TH inputs are
    jp nz,_IsJap    ; If the input does not match the output then it's a Japanese system

    ld a,%11111111  ; Set everything back to being inputs
    out ($3f),a

    ld a,0
    ret

_IsJap:
    ld a,1
    ret

Accessories

Schematics

 

René

Electronics engineer and retrogaming fanatic!