HuC6280 Assembly programming for the PC Engine! (TurboGrafx-16)

The PC-Engine uses a super-charged version of the 65c02... which itself is an improved version of the 6502

Known as the TurboGrafx-16, the PC-Engine is often mistaken for a 16 bit system because of its speed and graphical capability.

There are various successors to the PC engine, but we'll only be covering the basic model.

	PC Engine (TurboGrafx-16)
Cpu	1.79mhz HuC6280 (7.16 MHz fast mode)
Ram	8k
Vram	64k
Resolution	256x239 / 565x242
Sprites	64 onscreen, 16 per line (16x16 - 32x64)
Tilemap	32x32 (or higher)... max 2048 unique patterns
Colors	612 onscreen (16 per tile/sprite)
Sound chip	HuC6280 6 channel wavetable synthesis
CD	Optional CD drive
PSU	PAD-105: 9V Center Negative (10V Famicom adapter works) PAD-124: 10V Center Positive OTHERS MAY BE DIFFERENT! - see list here

ChibiAkumas Tutorials

	Lesson H9 - Hello World on the PC Engine/TurboGrafx-16 Card
	Lesson A1 - Extra commands in the 6280 (PC Engine) processor
	Lesson S9 - Bitmap Drawing on the on the PC Engine/TurboGrafx-16 Card
	Lesson S18 - Bitmap Drawing on the on the PC Engine/TurboGrafx-16 Card
	Lesson S30 - Tile Bitmap Clipping on the PC-Engine/Turbografix
	Lesson S31 - Hardware Sprite Clipping on the PC-Engine
	Lesson P5 - Bitmap Functions on the PC Engine (TurboGrafx-16)
	Lesson P14 - Joystick Reading on the PC Engine (TurboGrafx-16)
	Lesson P20 - Palette definitions on the PC Engine (TurboGrafx-16)
	Lesson P25 - Sound on the PC Engine (TurboGrafx-16)
	Lesson P33 - Hardware Sprites on the PC Engine (TurboGrafx-16)
	Lesson P48 - Sound on the PC Engine (ChibiSound Pro)
	Lesson P58 - Multiplatform Software tilemap on the PC Engine
	Lesson Photon8 - PC Engine - ASM PSET and POINT for Pixel Plotting

Resources

PC Engine Docs - A collection of PC Engine programming docs.
PC Engine GT Capacitor list - For repairing the portable PC Engine

The PC-Engine CPU banking and Memory Map

The PC engine uses an effective 21 bit memory map... 13 bits of the address specified, and 8 bits from the MPR register
The topmost 3 bits are mapped through a Memory Management unit which maps to Ram/Rom or hardware

This is all a bit confusing, but it's really pretty easy
This Memory management unit has 8 registers, each of which handles a range of $2000 of the memory map, and a bank from $00-$FF... $FF is the hardware I/O ... $F8 is the 8k of basic ram... $00 is the first page of your cartridge rom.

To page in a bank, we need to specify it by 'bit position' (so bank 7 has bit 7 set... so 128)
we load A with the bitmask for that MPR, then use the special command TAM (transfer A to MPR)

eg: - lets load bank $F8 into MPR page 1 ($2000-$3FFF)
lda #$F8 ;ram bank
TAM #2 ;bit 2 for bank 2 (%00000010)

NOTE: The ZeroPage is at $2000 , and the Stack is at $2100 ... this is unaffected by the MPR's.... this causes problems in VASM, where if we try to write STA $0000 ... the assembler will optimize it to STA $00

MPR	Setting	From	To	MPR Page
0	1	$0000	$1FFF	$FF (I/O)
1	2	$2000	$3FFF	$F8 (RAM)
2	4	$4000	$5FFF	????
3	8	$6000	$7FFF	????
4	16	$8000	$9FFF	????
5	32	$A000	$BFFF	????
6	64	$C000	$DFFF	????
7	128	$E000	$FFFF	$00 (Card Rom)

Segments

Bank	Purpose
$FF	I/O
$F9-$FB	SuperGrafx extra RAM (24k)
$F8	PC Engine RAM (8k)
$F7	Savegame RAM
$00-$F6	HuCard ROM

Vectors

From (Logical)	To (Logical)	Purpose
$FFF6	$FFF7	IRQ2 (External) / BRK
$FFF8	$FFF9	IRQ1 (VDC / Vblank)
$FFFA	$FFFB	Timer interrupt
$FFFC	$FFFD	NMI
$FFFE	$FFFF	-

From (Physical)	To (Physical)	Purpose
$00 1FFE	$00 1FFF	Reset

The Reset vector should be at $5FFE in your rom, and should contain "DW $E000" to start your program

IO Ports

Address	Purpose	Bits	Detail
$0000	GPU Reg Select (ST0)	NNNNNNNN	reg N
$0002	GPU Data L (ST1)	LLLLLLLL	Data L
$0003	GPU Data H (ST2)	HHHHHHHH	Data H
$0400	Palette: Reset	00000000	Write 0 to Reset
$0402	Palette: Palette Entry L	PPPPPPPP	Palette num (0-511)
$0403	Palette: Palette Entry H	-------P	Palette num (0-511)
$0404	Palette: New Color L	GGRRRBBB	Color
$0405	Palette: New Color H	-------G	Color
$0800	Channel Select	-----CCC	Channel Select
$0801	Main Amplitude Level	LLLLRRRR	L/R Volume
$0802	Frequency L	LLLLLLLL	Frequency botttom 8 bits
$0803	Frequency H	----HHHH	Frequency top 4 bits
$0804	Channel On/Write	ED-VVVVV	Enable (play)/write data... Direct digitaldata� channel Volume
$0805	LR Volume	LLLLRRRR	L/R Volume
$0806	Waveform Data	---WWWWW	Wave data (write 32 times)
$0807	Noise Enable	E--NNNNN	Enable noise� Noise freq (Chn 4/5 only)
$0808	LFO Freq	FFFFFFF	Noise freq (Chn 4/5 only)
$0809	LFO Control	T-----CC	lfo Trigger� Control
$1000	Joypad (Write)	------CS	C=CLR S=SEL
$1000	Joypad (Read)	-C--DDDD	C=Country D=Joypad Data
$1402	Interrupt Disable	-----T12	T=Timer interrupt request, 1= IRQ1 (Vblank), 2=IRQ2 (1=disabled)
$1403	Interrupt request	-----T12	T=Timer interrupt request, 1= IRQ1 (Vblank), 2=IRQ2 (1=occurred) Write any values to clear Timer interrupt (Vblank is cleared by reading VDC Status at $0100)
$1Ax0-$1Ax1	Data Port 0/1	DDDDDDDD	4 versions... Reg x (0-3)
$1Ax2-$1Ax4	Base address (24 bit)	$LLMMHH
$1Ax5-$1Ax6	Offset Register	$LLHH
$1Ax7-$1Ax8	Increment Register	$LLHH
$1Ax9	Control Register	SOOIoiNA	A=AutoInc N=iNdex offset + base i=increment is signed o=offset is signed I=apply increment to base(1) or offset(0)? OO=offset mode(None/Port0/Port1/Port0+1) S=Dataport size(0=Byte 1=Word)
$1AxA	Manual Register		Add offset to base
$1AE0-$1AE3		$LLMMHHUU	Work Register (32 bit)
$1AE4	Shift Register	----SSSS	Signed Shift for work register
$1AE5	Rotate Register	----RRRR	Signed Rotate for work register
$1AFE	AC card version	DDDDDDDD
$1AFF	AC ID	DDDDDDDD	$51=Present
$1C00	Timer Reload	-CCCCCCC	C=Counter
$1C01	Timer Control	-------S	Timer Start/Stop

The PC-Engine Graphics system

The PC Engine graphics hardware has 64k of ram... but it's designed for 128k... it's controlled by a set of registers... we have 3 hardware ports we use to control the hardware... these are usually memory mapped to $0000 ... but we also have special commands to quickly write fixed values to the graphics system

We ALWAYS write data to the graphics system registers in HL byte pairs... Little Endian, so low byte first.

To write data to the memory we set the address we want to write to with MAWR... but please note , we're only setting the last 16 of the 17 bits... for example, if we set MAWR to $3FFF (%11111111111111), the actual memory address will be %111111111111110

The effect is, that there are 2 bytes at VRAM $0000... and two bytes at VRAM $0001 ... and these bytes DO NOT OVERLAP!

Memory address	Command	Purpose
$0?00	ST0 xx	W= Select Register xx R = Status (%---------BVDSLOC) B=Busy V=Vblank D=Dma end S=SATB transfer end L=scanLine interrupt O=sprite Overflow (>16 sprites on a line) C=sprite Collision)
$0?02	ST1 xx	RW= Reg Val L=xx
$0?03	ST2 xx	RW= Reg Val H=xx

Reading from Status register (eg LDA $0100) clears Vblank interrupt - otherwise it will 'refire'.

Lets write &6543 to 'Byte Pair' at memory address &1234 (remember we always write in pairs):
        st0 0            ;Select Register 0 - to select memory address to write to
        st1 $34        ;Low byte of the memory address we want to write
        st2 $12        ;High byte of the memory address we want to write
        st0 2            ;Select Register 2 - to actually write data
        st1 $43        ;Low byte of data to put in memory
        st2 $65        ;High byte of data to put in memory

Graphics Registers

Reg	Name	Meaning	Bits
00	MAWR	Memory Address Write
01	MARR	Memory Address Read
02	VRR/VWR	Vram Data Write / Vram Data Read	(AutoIncs after Write)
03		Unused
04		Unused
05	CR	Control	- - - IW IW DR TE TE BB SB EX EX IE IE IE IE BB= Background on SB=Sprites on... IE bits 3-0 = Vblank / ScanLine match / SpriteOverflow / Collision
06	RCR	Scanning Line Detection
07	BXR	BGX Scroll
08	BYR	BGY Scroll
09	MWR	Memory Access Width	- - - - - - - - CM SCR SCR SCR SM SM WV WV (SCR=Screen Width /Height %YXX)
0A	HSR	Horizontal Sync
0B	HDR	Horizontal Display
0C	VPR	Vertical Sync
0D	BDW	Vertical Display
0E	BCR	Vertical Display End Position
0F	DCR	Block Transfer Control
10	SOUR	Block Transfer Source Address
11	DESR	Block Transfer Destination Address
12	LENR	Block Transfer Length
13	SATB	VRAM-SATB Block Transfer Source

VRAM Layout

Memory in the VRAM is not entirely fixed in purpose, this means you can have weird effects, like using the same memory area for your Tilemaps - and tile definitions (Patterns)... this is totally useless, as one will corrupt the other,
but we have to understand it's possible to understand the memory... as stated before, each address has 2 bytes...

A Pattern (tile definition) is 32 bytes in size (4 bitplanes, 8 lines)... and because each memory address in the VRAM map contains 2 bytes... the pattern will take up 16 memory addresses... this means tile 0 starts at $0000... and tile 1 is at $0010

NOW... the TileMap has to be at $0000 .. and it takes AT LEAST $0400 (it's minimum size is 32x32, and each definition takes 2 bytes)... so we can't use tiles 0-64
for ease, it's probably easiest to start your pattern definitions at no 256 (memory address $1000)

Vram From	Vram To	Purpose
$0000	$03FF	Min Tilemap (Tiles 0-63)
$0400	$0FFF	Possible Tilemap (Tiles 64-255)
$1000	$7FFF	Tiles 256-2048
$7F00	$7FFF	SATB sprite table
$8000	$FFFF	PC-Engine only has 64k, so this is unused

Palette Definitions
The PC engine uses two banks of 16 palettes of 16 colors each ... the first bank is for the tilemap (0-255), the second bank is for the sprites (256-511)

The Palette entries are controlled by special ports in the IO range in standard memory:
We write to $0402 and $0403 to select a palette entry, then define the new color for the palette entry by a 16 bit definition written to $0404 and $0405

F	E	D	C	B	A	9	8		7	6	5	4	3	2	1	0
-	-	-	-	-	-	-	G		G	G	R	R	R	B	B	B

Port	Purpose	7	6	5	4	3	2	1	0
$0400	Write 0 to Reset	0	0	0	0	0	0	0	0
$0402	Palette Entry L	P	P	P	P	P	P	P	P
$0403	Palette Entry H	-	-	-	-	-	-	-	P
$0404	New Color L	G	G	R	R	R	B	B	B
$0405	New Color H	-	-	-	-	-	-	-	G

Palette Entry	Purpose
0-255	Background
256-511	Sprites

Tilemap Definitions

As with everything else on the PC engine Vram... each tile definition takes one memory address, which contains 2 bytes...

The top 4 bits pppp define a 16 color palette number from 0-15...
The remaining 12 bits nnnn nnnnnnnn define the tile number -

as stated, the first 64-256 probably can't be used because they overlap the tilemap... no's 2048-4095 CANNOT be used, as the memory these would use would be 64k-128k... and this memory is not installed in the PC Engine.

ppppnnnn nnnnnnnn

Tile definitions
Tile definitions use 4 bitplanes for 16 colors, and tile definitions are 8x8 - so 32 bytes ... Data is transferred in Words, and rather strangely we send bitplane 1+2 of lines, one at a time... then we do the same for bitplanes 3 and 4

	Byte 1	Byte 2
First 16 bytes	00111100 01111111 01100011 01100011 01111111 01100011 01100011 00000000	00222200 02222222 02200022 02200022 02222222 02200022 02200022 00000000
Second 16 bytes	00333300 03333333 03300033 03300033 03333333 03300033 03300033 00000000	00444400 04444444 04400044 04400044 04444444 04400044 04400044 00000000

Sprite Definitions
The PC Engine has 64 hardware sprites. The basic sprite size is 16x16, though larger sprites can be created by tilling them, for up to 32x64.... only neighboring sprites can be tilled. Sprites use the second set of palettes, from 256-511

Sprites are NOT in the same format as the tilemap, they are 16x16 with 4 bitplanes, but each plane is sent separately.

For Example lets look at a sprite, where all pixels are color 0 or color 15!

First 16 writes (Bitplane 1)	1110000000000111 1000000100000001 1000000100000001 0000000100000000 0000000100000000 0000000100000000 0000000100000000 0000000111111100 0011111110000000 0000000010000000 0000000010000000 0000000010000000 0000000010000000 1000000010000001 1000000010000001 1110000000000111
Second 16 writes (Bitplane 2)	2220000000000222 2000000200000002 2000000200000002 0000000200000000 0000000200000000 0000000200000000 0000000200000000 0000000222222200 0022222220000000 0000000020000000 0000000020000000 0000000020000000 0000000020000000 2000000020000002 2000000020000002 2220000000000222

Third 16 writes (Bitplane 3)	3330000000000333 3000000300000003 3000000300000003 0000000300000000 0000000300000000 0000000300000000 0000000300000000 0000000333333300 0033333330000000 0000000030000000 0000000030000000 0000000030000000 0000000030000000 3000000030000003 3000000030000003 3330000000000333
Fourth 16 writes (Bitplane 4)	4440000000000444 4000000400000004 4000000400000004 0000000400000000 0000000400000000 0000000400000000 0000000400000000 0000000444444400 0044444440000000 0000000040000000 0000000040000000 0000000040000000 0000000040000000 4000000040000004 4000000040000004 4440000000000444

Sprites are stored in regular VRAM... the sprite definitions are stored in special ram which we CANNOT ACCESS...however we can allocate a bank of 256 addresses (each containing one word) called SATB, and then get the hardware to copy that ram to the special ram... it's suggested you use $7F00 for that purpose.

To start the copy we just write the address to control reg $13

SATB - Sprite attribute table buffer
The Sprite table allows for up to 64 sprites... each one has 4 words of data - making 256 words in total... the format is as follows

Address	F	E	D	C	B	A	9	8	7	6	5	4	3	2	1	0	Notes
1	-	-	-	-	-	-	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y=Ypos (64 is first visible line)
2	-	-	-	-	-	-	X	X	X	X	X	X	X	X	X	X	X=Xpos (32 is first visible line)
3	-	-	-	-	-	A	A	A	A	A	A	A	A	A	A	A	A=Address (Top 10 bits $trueaddress>>5 )
4	YF	-	YS	YS	XF	-	-	XS	F	-	-	-	P	P	P	P	YF=Yflip XF=Xflip YS=Ysize (16/32/64) XS=Xsize (16/32) F=Foreground (infront of tilemap) P=Palette (256+)

Joypad port at $1000
Joypad reading is performed with Port $1000. This port uses 4 bits for reading, so two reads from this port are needed to get the 8 buttons of a joypad. The PC Engine is capable of supporting up to 5 joypads, though we'll only read in two in these tutorials

Before we can start reading, we need to initialize the 'Multitap' (the hardware that toggles the joypads). Ro do this we just write a #1 then #3 to port $1000... we need a short delay after each write....

Once the Multitap is initialized, we can get the direction and button states by alternating writes of #1 and #0 to port $1000 - this will return the buttons of all 5 joysticks in order.

Joypad	Select bit (Bit 0 $1000)	7	6	5	4	3	2	1	0
1	1	CD addon (1=yes)	Country (0=jpn)	-	-	Left	Down	Right	Up
1	0	CD addon (1=yes)	Country (0=jpn)	-	-	Run	Start	B	A
2	1	CD addon (1=yes)	Country (0=jpn)	-	-	Left	Down	Right	Up
2	0	CD addon (1=yes)	Country (0=jpn)	-	-	Run	Start	B	A

The PC Engine actually supports 5 joypads, but Joypads 3-5 work in exatly the same way, we just need to keep reading in from the same port.

The PSG Sound generator

The PC Engine PSG has 6 wave based sound channels... each one uses 32 wave samples, of 5 bits each.

We have to snd some commands to $0804 to tell the PSG we're going to write data.. then send the data to $0806

We also need to set the volumes correctly!

To the right is a working example which will play a sound wave.

    lda #0
    sta $0800;Channel Select
    lda #255    ;Mixing
    sta $0801

    lda #1        ;Tone L
    sta $0802
    lda #10        ;Tone H
    sta $0803
    lda #%00011111    ;Chanel Op - Set 'Data Write'
    sta $0804
    lda #%01011111    ;Chanel Op - Set 'Reset Write Address'
    sta $0804

    lda #255
    sta $0805        ;LR Volume

    ldy #4
ChibiSoundMoreWaves:
    lda #%00011111
    sta $0806
    sta $0806
    sta $0806
    sta $0806
    lda #%00000000
    sta $0806
    sta $0806
    sta $0806
    sta $0806
    dey
    bne ChibiSoundMoreWaves

    lda #%10011111    ;Chanel Op - Set 'Play'
    sta $0804
     rts

Sound Registers

The PSG is controlled by 10 registers... first a channel should be selected with Register 0... Channels are numbered 0-5 (written 1-6 in the manuals)

Reg

Address

Meaning

Channels

Bit Meaning

$0800

Channel Select

All

Channel Select

$0801

Main Amplitude Level

All

L/R Volume

$0802

Frequency L

0-5

Frequency botttom 8 bits

$0803

Frequency H

0-5

Frequency top 4 bits

$0804

Channel On/Write

0-5

Enable (play)/write data... Direct digitaldata� channel Volume

$0805

LR Volume

0-5

L/R Volume

$0806

Waveform Data

0-5

Wave data (write 32 times)

$0807

Noise Enable

0-5

Enable noise� Noise freq (Chn 4/5 only)

$0808

LFO Freq

All

lfo Frequency

$0809

LFO Control

All

lfo Trigger� Control