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Main.asm
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; =======================
; Rebound GBC main source
; =======================
; If set to 1, enable debugging features.
DebugMode = 1
; Defines
include "Defines.asm"
; =============
; Reset vectors
; =============
section "Reset $00",rom0[$00]
Bankswitch:: jp _Bankswitch
section "Reset $08",rom0[$08]
FillRAM:: jp _FillRAM
section "Reset $10",rom0[$10]
WaitVBlank:: jp _WaitVBlank
section "Reset $18",rom0[$18]
WaitTimer:: jp _WaitTimer
section "Reset $20",rom0[$20]
WaitLCDC:: jp _WaitLCDC
section "Reset $30",rom0[$30]
DoOAMDMA:: jp $ff80
section "Reset $38",rom0[$38]
Trap:: jr @
; ==================
; Interrupt handlers
; ==================
section "VBlank IRQ",rom0[$40]
IRQ_VBlank:: jp DoVBlank
section "STAT IRQ",rom0[$48]
IRQ_Stat:: jp DoStat
section "Timer IRQ",rom0[$50]
IRQ_Timer:: jp DoTimer
section "Serial IRQ",rom0[$58]
IRQ_Serial:: jp DoSerial
section "Joypad IRQ",rom0[$60]
IRQ_Joypad:: jp DoJoypad
; ===============
; System routines
; ===============
; ================================================================
; Call HL
; ================================================================
_CallHL:
ld a,h
bit 7,a
jr nz,@ ; trap
.skip
jp hl
; ==========
; ROM header
; ==========
section "ROM header",rom0[$100]
EntryPoint::
nop
jp ProgramStart
if !def(BUILD_POCKET)
NintendoLogo: ds 48,0 ; Nintendo logo bitmap (handled by post-linking tool)
else
AnalogueLogo:
db $01,$10,$CE,$EF,$00,$00,$44,$AA,$00,$74,$00,$18,$11,$95,$00,$34
db $00,$1A,$00,$D5,$00,$22,$00,$69,$6F,$F6,$F7,$73,$09,$90,$E1,$10
db $44,$40,$9A,$90,$D5,$D0,$44,$30,$A9,$21,$5D,$48,$22,$E0,$F8,$60
endc
ROMTitle: dbp "REBOUND",15,0 ; ROM title (15 bytes)
GBCSupport: db $C0 ; GBC support (0 = DMG only, $80 = DMG/GBC, $C0 = GBC only)
NewLicenseCode: db "56" ; new license code (2 bytes)
SGBSupport: db 0 ; SGB support
CartType: ; Cart type, see hardware.inc for a list of values
if DebugMode
db $1b
else
db $19
endc
ROMSize: db 0 ; ROM size (handled by post-linking tool)
RAMSize: ; RAM size
if DebugMode
db 2 ; 8k sram for tilemap editor
else
db 0
endc
DestCode: db 1 ; Destination code (0 = Japan, 1 = All others)
OldLicenseCode: db $33 ; Old license code (if $33, check new license code)
ROMVersion: db 0 ; ROM version
HeaderChecksum: db 0 ; Header checksum (handled by post-linking tool)
ROMChecksum: dw 0 ; ROM checksum (2 bytes) (handled by post-linking tool)
; =====================
; Start of program code
; =====================
section fragment "Program code",rom0[$150]
ProgramStart::
di
ld sp,$d000
; preserve A and B for later to determine console type
push bc
push af
; wait for VBlank before disabling LCD
ld hl,rLY
ld a,SCRN_Y
.wait
cp [hl]
jr nz,.wait
xor a
ldh [rLCDC],a ; disable LCD
ld [sys_PauseGame],a
ld a,60
ld [sys_SleepModeTimer],a
ld [sys_SecondsUntilSleep],a
farcall DevSound_Stop ; prevent glitch music from playing
; clear HRAM
ld bc,$7f80
xor a
.loop
ld [c],a
inc c
dec b
jr nz,.loop
call CopyDMARoutine
call ClearScreen
; check GB type
; sets sys_GBType to 0 if DMG/SGB/GBP/GBL/SGB2, 1 if GBC, 2 if GBA/GBA SP/GB Player
pop af
pop bc
cp $11
jp nz,GBCOnlyScreen
.gbc
and 1 ; a = 1
add b ; b = 1 if on GBA
ld [sys_GBType],a
; spoof check!
; makes use of a register that only exists in CGB mode (namely the VRAM bank register)
ld hl,_VRAM
ld [hl],a
ld b,a
ld a,1
ldh [rVBK],a ; rVBK is not supported on DMG
ld a,b
cp [hl]
jr z,GBCOnlyScreen
xor a
ld [rVBK],a
; emulator check!
; uses echo RAM - any write to WRAM will reflect in echo RAM and vice versa
ld a,b
ld [sys_EmuCheck],a ; store value
ld a,[sys_EmuCheck+$2000] ; read value back from echo RAM
cp b ; do they match?
jp z,SkipGBCScreen ; if yes, emulator check passed
EmuScreen: ; otherwise, emulator check failed
ldfar hl,Pal_DebugScreen
xor a
call LoadPal
call CopyPalettes
ldfar hl,Font
ld de,$8000
call DecodeWLE
ldfar hl,EmuText
call LoadTilemapText
ld a,LCDCF_ON | LCDCF_BG8000 | LCDCF_BGON
ldh [rLCDC],a
ld a,IEF_VBLANK
ldh [rIE],a
ei
: halt
jr :- ; infinite loop
GBCOnlyScreen:
xor a
ld [sys_GBType],a
; GBC only screen
SetDMGPal rBGP,0,3,3,0
ldfar hl,Font
ld de,$8000
call DecodeWLE
ldfar hl,GBCOnlyText
call LoadTilemapText
ld a,LCDCF_ON | LCDCF_BG8000 | LCDCF_BGON
ldh [rLCDC],a
ld a,IEF_VBLANK
ldh [rIE],a
: halt
jr :- ; infinite loop
section "DMG and emulator lockout screen text",romx
GBCOnlyText: ; 20x18 char tilemap
db " "
db " - REBOUND! - "
db " "
db " THIS GAME WILL "
db " ONLY WORK ON A "
db " GAME BOY COLOR "
db " OR A GAME BOY "
db " ADVANCE. "
db " "
db " PLEASE USE A "
db " GAME BOY COLOR "
db " OR A GAME BOY "
db " ADVANCE TO "
db " PLAY THIS GAME. "
db " "
db " "
db " "
db " "
EmuText:
db " "
db " - REBOUND! - "
db " "
db " "
db " "
db " THIS GAME WILL "
db " NOT WORK IN YOUR "
db " EMULATOR. "
db " "
db " PLEASE USE A "
db " NEWER EMULATOR "
db " SUCH AS SAMEBOY OR "
db " BGB TO PLAY THIS "
db " GAME. "
db " "
db " "
db " "
db " "
section fragment "Program code",rom0
; ========================================================================
SkipGBCScreen:
; clear vars
xor a
ld [sys_ResetTimer],a
ld [sys_CurrentFrame],a
ld [sys_btnPress],a
ld [sys_btnHold],a
ld [sys_VBlankFlag],a
ld [sys_TimerFlag],a
ld [sys_LCDCFlag],a
ld [VGMSFX_Flags],a
ld [Engine_CameraX],a
ld [Engine_CameraY],a
ld [sys_EnableHDMA],a
ld [Player_CoinCount],a
ld [Player_CoinCount+1],a
ld [Player_CoinCountHUD],a
ld [Player_CoinCountHUD+1],a
call DoubleSpeed
if !DebugMode
jp GM_SplashScreens
else
jp GM_DebugMenu
endc
; ================================
include "Engine/GameModes/DebugMenu.asm"
; ================================
include "Engine/GameModes/SplashScreens.asm"
; ================================
include "Engine/GameModes/TitleAndMenus.asm"
; ================================
include "Engine/GameModes/SoundTest.asm"
; ================================
include "Engine/GameModes/SFXTest.asm"
; ================================
include "Engine/GameModes/LevelSelect.asm"
; ================================
include "Engine/GameModes/Level.asm"
; ================================
include "Engine/GameModes/Credits.asm"
; ================================
include "Engine/GameModes/EndScreen.asm"
; ================================
include "Engine/GameModes/GameOverScreen.asm"
; ================================
include "Engine/GameModes/Gallery.asm"
; ================================
include "Engine/GameModes/MetatileViewer.asm"
; ================================
; ==================
; Interrupt handlers
; ==================
section "Interrupt handlers",rom0
DoVBlank::
push af
push bc
push de
push hl
ld a,1
ld [sys_VBlankFlag],a ; set VBlank flag
call UpdatePalettes
ld a,[sys_PauseGame]
and a ; is game paused?
jr nz,:+ ; if yes, skip frame counter tick
ld a,[sys_CurrentFrame]
inc a
ld [sys_CurrentFrame],a ; tick frame counter
:
; check input
ld a,[sys_btnHold]
ld c,a
ld a,P1F_5
ldh [rP1],a
ldh a,[rP1]
ldh a,[rP1]
cpl
and $f
swap a
ld b,a
ld a,P1F_4
ldh [rP1],a
ldh a,[rP1]
ldh a,[rP1]
ldh a,[rP1]
ldh a,[rP1]
ldh a,[rP1]
ldh a,[rP1]
cpl
and $f
or b
ld b,a
ld a,[sys_btnHold]
xor b
and b
ld [sys_btnPress],a ; store buttons pressed this frame
ld e,a
ld a,b
ld [sys_btnHold],a ; store held buttons
xor c
xor e
ld [sys_btnRelease],a ; store buttons released this frame
ld a,P1F_5|P1F_4
ld [rP1],a
: ; setup HDMA for parallax GFX transfer
ld a,[sys_EnableHDMA]
and a
jr z,.skiphdma ; skip ahead if HDMA is disabled
xor a
ldh [rVBK],a
ld a,high(Engine_ParallaxBuffer)
ldh [rHDMA1],a ; HDMA source high
ld a,low(Engine_ParallaxBuffer)
ldh [rHDMA2],a ; HDMA source low
ld a,[Engine_ParallaxDest]
ldh [rHDMA3],a ; HDMA dest high
xor a
ldh [rHDMA4],a ; HDMA dest low
ld a,%00001111
ldh [rHDMA5],a ; HDMA length + type (length 256, hblank wait)
; wait for transfer to finish
: ldh a,[rHDMA5]
inc a ; rHDMA5 = $FF? (indicates HDMA transfer is finished)
jr nz,:- ; if not, wait until it is
; setup HDMA for player GFX transfer
ld a,[sys_HDMABank]
ld b,a
call _Bankswitch
ld a,1
ldh [rVBK],a
ld a,[sys_HDMA1]
ldh [rHDMA1],a
ld a,[sys_HDMA2]
ldh [rHDMA2],a
ld a,[sys_HDMA3]
ldh [rHDMA3],a
ld a,[sys_HDMA4]
ldh [rHDMA4],a
ld a,[sys_HDMA5]
ldh [rHDMA5],a
.skiphdma
; set camera position
ld a,[Engine_CameraX]
ldh [rSCX],a
ld a,[Engine_CameraY]
ldh [rSCY],a
rst DoOAMDMA
; A+B+Start+Select restart sequence
ld a,[sys_btnHold]
cp _A+_B+_Start+_Select ; is A+B+Start+Select pressed?
jr nz,.noreset ; if not, skip
ld a,[sys_ResetTimer] ; get reset timer
inc a
ld [sys_ResetTimer],a ; store reset timer
cp 60 ; has 1 second passed?
jr nz,.continue ; if not, skip
ld a,[sys_GBType] ; get current GB model
dec a ; GBC?
jr z,.gbc ; if yes, jump
dec a ; GBA?
jr z,.gba ; if yes, jump
.dmg ; default case: assume DMG
xor a ; a = 0, b = whatever
jr .dorestart
.gbc ; a = $11, b = 0
ld a,$11
ld b,0
jr .dorestart
.gba ; a = $11, b = 1
ld a,$11
ld b,1
; fall through to .dorestart
.dorestart
ld hl,rHDMA5
set 0,[hl] ; cancel any pending HDMA transfers
jp ProgramStart ; restart game
.noreset ; if A+B+Start+Select aren't held...
xor a
ld [sys_ResetTimer],a ; reset timer
.continue ; done
; sound update
ld a,[sys_PauseGame]
and a
jr nz,:+ ; don't update music if game is paused
farcall DevSound_Play
: call VGMSFX_Update ; *do* update SFX while game is paused (for pause sound)
call Pal_DoFade ; do palette fading
pop hl
pop de
pop bc
pop af
reti ; done!
DoStat::
push af
ld a,1
ld [sys_LCDCFlag],a
pop af
reti
; Currently not used
DoTimer::
push af
ld a,1
ld [sys_TimerFlag],a
pop af
reti
; Currently not used
DoSerial::
push af
ld a,1
ld [sys_SerialFlag],a
pop af
reti
; Currently not used
DoJoypad::
push af
ld a,1
ld [sys_JoypadFlag],a
pop af
reti
; =======================
; Interrupt wait routines
; =======================
; Wait for vertical blank.
_WaitVBlank::
push af
ldh a,[rIE]
bit 0,a
jr z,.done
.wait
halt
ld a,[sys_VBlankFlag]
and a
jr z,.wait
xor a
ld [sys_VBlankFlag],a
.done
pop af
ret
; Wait for LCD status interrupt.
_WaitLCDC::
push af
ldh a,[rIE]
bit 1,a
jr z,.done
.wait
halt
ld a,[sys_LCDCFlag]
and a
jr z,.wait
xor a
ld [sys_LCDCFlag],a
.done
pop af
ret
; Wait for timer interrupt. (Currently unused)
_WaitTimer::
push af
ldh a,[rIE]
bit 2,a
jr z,.done
.wait
halt
ld a,[sys_TimerFlag]
and a
jr z,.wait
xor a
ld [sys_VBlankFlag],a
.done
pop af
ret
; Wait for serial transfer interrupt. (Currently unused)
_WaitSerial::
push af
ldh a,[rIE]
bit 3,a
jr z,.done
.wait
halt
ld a,[sys_SerialFlag]
and a
jr z,.wait
xor a
ld [sys_SerialFlag],a
.done
pop af
ret
; Wait for joypad interrupt. (Currently unused)
_WaitJoypad:
push af
ldh a,[rIE]
bit 4,a
jr z,.done
.wait
halt
ld a,[sys_JoypadFlag]
and a
jr z,.wait
xor a
ld [sys_JoypadFlag],a
.done
pop af
ret
; =================
; Graphics routines
; =================
include "Engine/PerFade.asm" ; Palette routines
; =========
; Clear the screen.
; TRASHES: a, bc, hl
; RESTRICTIONS: Requires the LCD to be disabled, otherwise screen will not be properly cleared.
ClearScreen:
xor a
ldh [rHDMA5],a ; cancel pending HDMA transfers (do this before actually clearing VRAM)
; clear VRAM bank 0
xor a
ldh [rVBK],a
ld hl,_VRAM ; clear from start of VRAM...
ld bc,_SRAM-_VRAM ; ...to end of VRAM.
rst FillRAM
; clear VRAM bank 1
ld a,1
ldh [rVBK],a
ldh [sys_TempSVBK],a
xor a
ld hl,_VRAM ; clear from start of VRAM...
ld bc,_SRAM-_VRAM ; ...to end of VRAM.
rst FillRAM
xor a
ldh [rVBK],a
; clear OAM
ld hl,OAMBuffer
ld b,OAMBuffer.end-OAMBuffer
xor a
call _FillRAMSmall
; clear palette buffers
xor a
ld hl,sys_PalTransferBuf
ld bc,sys_PalBuffersEnd-sys_PalTransferBuf
rst FillRAM
; reset scrolling
xor a
ldh [rSCX],a
ldh [rSCY],a
ld [Engine_CameraX],a
ld [Engine_CameraY],a
ld [sys_EnableHDMA],a
ret
; Same as ClearScreen, but preserves loaded graphics.
ClearScreen2:
xor a
ldh [rHDMA5],a ; cancel pending HDMA transfers (do this before actually clearing VRAM)
; clear VRAM bank 0
xor a
ldh [rVBK],a
ld hl,_SCRN0 ; clear from start of VRAM...
ld bc,_SRAM-_SCRN0 ; ...to end of VRAM.
rst FillRAM
; clear VRAM bank 1
ld a,1
ldh [rVBK],a
ldh [sys_TempSVBK],a
xor a
ld hl,_SCRN0 ; clear from start of VRAM...
ld bc,_SRAM-_SCRN0 ; ...to end of VRAM.
rst FillRAM
xor a
ldh [rVBK],a
; clear OAM
ld hl,OAMBuffer
ld b,OAMBuffer.end-OAMBuffer
xor a
call _FillRAMSmall
; clear palette buffers
xor a
ld hl,sys_PalTransferBuf
ld bc,sys_PalBuffersEnd-sys_PalTransferBuf
rst FillRAM
; reset scrolling
xor a
ldh [rSCX],a
ldh [rSCY],a
ld [Engine_CameraX],a
ld [Engine_CameraY],a
ld [sys_EnableHDMA],a
ret
; Loads a 20x18 tilemap to VRAM.
; INPUT: hl = source
; TRASHES: a, bc, de, hl
; RESTRICTIONS: Must run during VBlank or while VRAM is accessible, otherwise written data will be corrupted
LoadTilemapScreen:
ld de,_SCRN0
lb bc,$12,$14
.loop
ld a,[hl+]
ld [de],a
inc de
dec c
jr nz,.loop
ld c,$14
ld a,e
add $c
jr nc,.continue
inc d
.continue
ld e,a
dec b
jr nz,.loop
ret
; Same as LoadTilemapScreen, but performs ASCII conversion.
; INPUT: hl = source
; TRASHES: a, bc, de, hl
; RESTRICTIONS: Must run during VBlank or while VRAM is accessible, otherwise written data will be corrupted
LoadTilemapText:
ld de,_SCRN0
lb bc,$12,$14
.loop
ld a,[hl+]
sub " "
ld [de],a
inc de
dec c
jr nz,.loop
ld c,$14
ld a,e
add $C
jr nc,.continue
inc d
.continue
ld e,a
dec b
jr nz,.loop
ret
; Prints a null-terminated string.
; INPUT: hl = source
; de = destination
PrintString:
WaitForVRAM
ld a,[hl+]
and a ; terminator byte reached?
ret z ; if yes, return
sub " "
ld [de],a
inc de
jr PrintString
; ============
; Sprite stuff
; ============
; Copies OAM DMA routine to HRAM.
; Called once during startup sequence.
; TRASHES: a, bc, hl
CopyDMARoutine::
ld bc,low(OAM_DMA) + ((_OAM_DMA_End-_OAM_DMA) << 8)
ld hl,_OAM_DMA
.loop
ld a,[hl+]
ld [c],a
inc c
dec b
jr nz,.loop
ret
; OAM DMA routine.
; This is copied to HRAM by CopyDMARoutine and run from there.
; TRASHES: a
_OAM_DMA::
ld a,high(OAMBuffer)
ldh [rDMA],a
ld a,$28
.wait ; wait for OAM DMA to finish
dec a
jr nz,.wait
ret
_OAM_DMA_End:
include "Engine/Sprite.asm" ; Sprite routines
; =============
; Misc routines
; =============
; include "Engine/GBPrinter.asm"
; ================
; Performs a bankswitch to bank B, preserving previous ROM bank.
; INPUT: b = bank
_Bankswitch:
push af
ldh a,[sys_CurrentBank]
ldh [sys_LastBank],a ; preserve old ROM bank
ld a,b
ldh [sys_CurrentBank],a ; set new ROM bank
ld [rROMB0],a ; perform bankswitch
pop af
ret
; Fill RAM with a value.
; INPUT: a = value
; hl = address
; bc = size
; TRASHES: a, bc, e, hl
_FillRAM::
ld e,a
.loop
ld [hl],e
inc hl
dec bc
ld a,b
or c
jr nz,.loop
ret
; Fill up to 256 bytes of RAM with a value.
; INPUT: a = value
; hl = address
; b = size
; TRASHES: a, b, e, hl
_FillRAMSmall::
ld e,a
.loop
ld [hl],e
inc hl
dec b
jr nz,.loop
ret
; ================
; Copy up to 65536 bytes to RAM.
; INPUT: hl = source
; de = destination
; bc = size
; TRASHES: a, bc, de, hl
_CopyRAM::
ld a,[hl+]
ld [de],a
inc de
dec bc
ld a,b
or c
jr nz,_CopyRAM
ret
; Copy up to 256 bytes to RAM.
; INPUT: hl = source
; de = destination
; b = size
; TRASHES: a, b, de, hl
_CopyRAMSmall::
ld a,[hl+]
ld [de],a
inc de
dec b
jr nz,_CopyRAMSmall
ret
; ================
; Switches double speed mode on.
; TRASHES: a
DoubleSpeed:
ldh a,[rKEY1]
bit 7,a ; already in double speed?
ret nz ; if yes, return
ld a,%00110000
ldh [rP1],a
xor %00110001 ; a = %00000001
ldh [rKEY1],a ; prepare speed switch
stop
ret
include "Engine/WLE_Decode.asm"
; =============
; Misc routines
; =============
; Calculate a sine wave.
; INPUT: a = angle
; OUTPUT: d = cosine
; e = sine
; TRASHES: bc, hl, flags, ROM bank
GetSine:
ldfar hl,SineTable
ld c,a
ld b,0
add hl,bc
ld d,[hl]
ld hl,CosineTable
add hl,bc
ld e,[hl]
resbank
ret
section "Sine table",romx
SineTable:
db 0, 3, 6, 9, 12, 16, 19, 22, 25, 28, 31, 34, 37, 40, 43, 46
db 49, 52, 55, 57, 60, 63, 66, 68, 71, 73, 76, 78, 81, 83, 86, 88
db 90, 92, 94, 97, 99, 101, 102, 104, 106, 108, 109, 111, 112, 114, 115, 117
db 118, 119, 120, 121, 122, 123, 124, 124, 125, 126, 126, 127, 127, 127, 127, 127
CosineTable:
db 127, 127, 127, 127, 127, 127, 126, 126, 125, 124, 124, 123, 122, 121, 120, 119
db 118, 117, 115, 114, 112, 111, 109, 108, 106, 104, 102, 101, 99, 97, 94, 92
db 90, 88, 86, 83, 81, 78, 76, 73, 71, 68, 66, 63, 60, 57, 55, 52
db 49, 46, 43, 40, 37, 34, 31, 28, 25, 22, 19, 16, 12, 9, 6, 3
db 0, -3, -6, -9, -12, -16, -19, -22, -25, -28, -31, -34, -37, -40, -43, -46
db -49, -52, -55, -57, -60, -63, -66, -68, -71, -73, -76, -78, -81, -83, -86, -88
db -90, -92, -94, -97, -99,-101,-102,-104,-106,-108,-109,-111,-112,-114,-115,-117
db -118,-119,-120,-121,-122,-123,-124,-124,-125,-126,-126,-127,-127,-127,-127,-127
db -127,-127,-127,-127,-127,-127,-126,-126,-125,-124,-124,-123,-122,-121,-120,-119
db -118,-117,-115,-114,-112,-111,-109,-108,-106,-104,-102,-101, -99, -97, -94, -92
db -90, -88, -86, -83, -81, -78, -76, -73, -71, -68, -66, -63, -60, -57, -55, -52
db -49, -46, -43, -40, -37, -34, -31, -28, -25, -22, -19, -16, -12, -9, -6, -3
db 0, 3, 6, 9, 12, 16, 19, 22, 25, 28, 31, 34, 37, 40, 43, 46
db 49, 52, 55, 57, 60, 63, 66, 68, 71, 73, 76, 78, 81, 83, 86, 88
db 90, 92, 94, 97, 99, 101, 102, 104, 106, 108, 109, 111, 112, 114, 115, 117
db 118, 119, 120, 121, 122, 123, 124, 124, 125, 126, 126, 127, 127, 127, 127, 127
section "Misc routines",rom0
include "Engine/Metatile.asm"
include "Engine/Parallax.asm"
include "Engine/Player.asm"
include "Engine/Object.asm"
; 16-bit Compare
; INPUT: bc = value 1
; de = value 2
; OUTPUT: zero = set if equal
; carry = set if bc < de
; TRASHES: a
Compare16:
ld a,b
cp d
ret nz
ld a,c
cp e
ret
; INPUT: a = hexadecimal number
; OUTPUT: sys_StringBuffer = converted number
; TRASHES: bc, hl
; Adapted from https://wikiti.brandonw.net/index.php?title=Z80_Routines:Other:DispA
Hex2Dec8:
ld hl,sys_StringBuffer
ld c,-100
call :+ ; hundreds place
ld c,-10
call :+ ; tens place
ld c,-1
: ld b,-1
: inc b
add c
jr c,:-
sub c
push af
ld a,b
ld [hl+],a
pop af
ret
; INPUT: hl = decimal number
; OUTPUT: sys_StringBuffer = hexadecimal number
; TRASHES: a, bc, de, hl
; Adapted from https://wikiti.brandonw.net/index.php?title=Z80_Routines:Other:DispHL
Hex2Dec16:
ld de,sys_StringBuffer
ld bc,-10000
call :+ ; ten-thousands place