hello.z80

#include    "ti83plus.inc"
#define     progStart   $9D95
.org        progStart-2
.db         $BB,$6D
    ld de, $9D95 ;the address we're viewing (starts at the prog start just because)
    ld hl, $0000
    ld ($844B), hl ;make curRow and curCol 0 for PutS

    ;display the address
    ld hl, $93B0
    ld a, d
    call Output1
    ld a, e
    call Output1

    ld (hl), $00 ;null terminate the string
    ld hl, $9340
    ld b, $38
loop: ;main loop for displaying 0x38 bytes onscreen
    ld a, (de)
    call Output1
    inc de
    djnz loop

    push de
    ld hl, $9340
    bcall(_PutS)
    bcall(_GetKey) ;waits for keypress

    cp $05 ;exit on enter
    ret z

    ld de, $FFC8 ;default value for screen movement (goes back up after we displayed 0x38 bytes of memory)

    ;ensure key is 1, 2, 3, 4, 80, 81, 82, or 83 for moving the screen around
    rlca ;a is now 1, 2, 3, 4, 5, 6, 7, or 8
    cp $01
    jr c, nomove
    cp $09
    jr nc, nomove
    add a, a
    add a, MoveTable-2-$9E00 ;as long as MoveTable is 9Exx this will work
    ld l, a
    adc a, (MoveTable-2)/256 ;this one doesn't depend on it being 9Exx >.>
    sub l
    ld h, a
    ld d, (hl)
    inc hl
    ld e, (hl)
    ;pushed the address into de earlier, we use hl for this and make de the offset
    ;later we pop hl to add them up

nomove:
    ;de is FFC8 for not moving the screen

    pop hl ;hl was the address, de is the offset for this addition
    add hl, de
    ld d,h
    ld e,l

    ;next handle editing memory values
    cp $85 ;left paren = decrement
    .db $20, $01 ;jr nz +1
    dec (hl)

    cp $86 ;right paren = increment
    .db $20, $01
    inc (hl)

    cp $B9 ;cos = -10
    .db $20, $05
    ld b, $10
    dec (hl)
    .db $10, $FD ;djnz -3

    cp $BB ;tan = +10
    .db $20, $05
    ld b, $10
    inc (hl)
    .db $10, $FD ;djnz -3

    jp $9D98
Output1:
    ld c, a
    rrca
    rrca
    rrca
    rrca
    call Output2
Output2:
    and $0F
    add a, $30
    cp $3A
    .db $38, $02 ;jr c +2
    add a, $07
    ld (hl), a
    inc hl
    ld a, c
    ret

MoveTable:
.dw $0FC8 ;plus = +1000
.dw $FFC9 ;right = +1
.dw $EFC8 ;minus = -1000
.dw $FFC7 ;left = -1
.dw $00C8 ;mult = +100
.dw $FFC0 ;up = -8 (1 row)
.dw $FEC8 ;div = -100
.dw $FFD0 ;down = +8 (1 row)