link.asm

;(Just a note)
;(The 83+ link port works very simply (the rest should be like this))
;(Line 0 is bit 0)
;(Line 1 is bit 1)
;(It works the same for input and output)
;
; SOME VERY NICE LINK ROUTINES MADE BY PASCAL BOURON
;
; I've made some modifications so it fits ZTetris
;
; Ported to TI83 and highly optimized by Florent Dhordain 06/04/98 MMDDYY
;


ReceiveByte:
    ld l,0              ; l used as lcounter
    ld b,8              ; 8 bits to receive
    ;ld a,$D0           ; (reset the port to high both lines)
    ld a,0
    out (0),a
rb_w_Start:
    in a,(0)
    ;and $C
    ;cp $C              ; wait one line becomes low
    and    3            ; (check if either line is low)
    cp    3
    jr nz,rb_get_bit
    kcall(Test_ON)
    jr rb_w_Start
rb_get_bit:
    ld l,0              ; reset lcounter
    ;cp 8               ; is it a 0 ? (is line1 low?)
    cp 2
    jr z,rb_receive_zero    ; Yeah !
    ;ld a,$D1
    ld    a,1
    out (0),a           ; Ack for a '1'
    rr c                ; put the 1 (cf has been set by cp)
rb_waitstop1:
    kcall(Test_On)
    in a, (0)
    ;and $8             ; wait 'til Ack is recognized
    and 2               ; (line1 pulled low?)
    jr z, rb_waitstop1
    jr rb_stopok

rb_receive_zero:
    ;ld a,$d2           ; Ack for a '0'
    ld a,2
    out (0),a           ; (pull line1 low)
    rr c                ; put the 0 (cf has been cleared by cp)
rb_waitStop0:
    kcall(Test_On)
    in a,(0)
    ;and $4             ; wait 'til Ack is recognized
    and 1               ; (is line0 low (the ack))
    jr z,rb_waitStop0
rb_stopok:              ; here, one line is low cause of us(recv)
    ;ld a,$d0           ; the sender calc has already set lines to hi
    ld a,0              ; (reset port to lines high)
    out (0),a
    djnz rb_w_Start
    ld a,c
    ret

Test_ON:
    dec l
    ret nz              ; exit only if cnt = 0
    pop hl              ;Back to the place you were before.    Gotta love it!
    ;ld a, $d0
    ld a,0
    out (0), a
    xor a
    ret

SendByte:
    ld hl,0
    ld (ix + lcounter), l
    ld (ix + lcounter +1), h
    ld b,8
    ld c,a              ; byte to send (using bit rotates into carry to find bit to send)
    ld d, a             ; Save it
    ;ld a,$D0
    ld a,0              ; (reset port to all high)
    out (0),a
w_setport3:
    in a,(0)
    ;and $C
    ;cp $C              ; wait both lines are low
    and 3               ; (are either line low?)
    cp 3
    jr z, calc_bit
    kcall(SendTest_ON)
    jr w_setport3
calc_bit:
    rr c                ; (is the next bit to send a 1 or 0?)
    ;ld a, $d2
    ld a,2
    jr c,send_one       ; (if its a 1, goto send_one)
send_zero:
    dec a
send_one:
    out (0),A
wait_setport:
    kcall(SendTest_ON)
    in a,(0)
    ;and $C             ; wait both become low
    and 3               ; (are both lines low?)
    jr nz,wait_setport
    ;ld a,$D0           ; put them back to hi
    ld a,0              ; (reset both lines to high)
    out (0),A
    djnz w_setport3
    ld a,d              ; Restore byte
    ret

SendTest_ON:
    ld a,(ix + hsflag)
    or a
    jr z,LongWait
    ;bcall(_getk)       ; dunno, I don't have a getk equate
    ;cp $09
    pcall(getKey)
    cp kMode            ; If this is clear, exit !
    ret nz
    pop hl
    pop hl
    kjp(Quit)
LongWait:
    ld l, (ix + lcounter)
    ld h, (ix + lcounter + 1)
    inc hl
    ld (ix + lcounter), l
    ld (ix + lcounter + 1), h
    bit 6, h            ; Has the counter reached $4000
    ret z               ; no, continue
    pop hl
    ret