hello.z80

#define     WRTPSG   $0093
#define     RDPSG   $0096

.org        $c000

TYPE        .db     $fe
ADDRSTART   .dw     $c000
ADDREND     .dw     (END)
ADDREXE     .dw     $c009

LO          .db     $00
HI      .db     $00

.org        $c009

    call    READJOYPORTLO
    and $3F
    ld  c,a     ; c=0,0,C,B,L,R,D,U

    call    READJOYPORTHI
    and $3C     ; crop S,A,I,I
    add a,a
    add a,a
    ld  b,a     ; b=S,A,I,I,0,0,0,0

    call    READJOYPORTLO
    call    READJOYPORTHI
    call    READJOYPORTLO
    call    READJOYPORTHI
    and 00001111b   ; 2nd ID = 0?
    jr  nz,joy3btn  ; If this joypad isn't the 6-button model, skip

    ld  a,b     ; a=S,A,0,0,0,0,0,0
    or  c       ; a=S,A,C,B,R,L,D,U
    ld  c,a     ; c=S,A,C,B,R,L,D,U
    call    READJOYPORTLO   ;   ?,?,C,B,M,X,Y,Z
    and $0F     ; Crop      M,X,Y,Z
    ld  b,a     ; b=0,0,0,0,M,X,Y,Z
    ld  (LO),a
    ld  a,c     ; a=S,A,C,B,R,L,D,U
    ld  (HI),a
    ret
joy3btn:    ; This is a 3-button joypad
    ; Now place the bits in the standard two-byte format used for all Sega
    ; controllers & multi-tap
    ld  a,b     ; a=ST,A,00,0000
    or  c       ; a=ST,A,C,B,Rt,Lt,Dn,Up
    ld  b,$1F   ; b=JOYID:001,11111 (L=MODE=X=Y=Z=1)
    ret

READJOYPORTHI:
    ld  e,$9F
    ld  a,15
    jp  WRTPSG
    jp  READJOYPORT
READJOYPORTLO:
    ld  e,$8F
    ld  a,15
    jp  WRTPSG
    jp  READJOYPORT
READJOYPORT:
    ld  a,14
    di
    call    RDPSG
    ei
    ret

END: