PC-9821

While the West had the IBM PC's, Japan decided to go a different route!

Starting with the PC-8800 (PC-88) series and 8086 processors, and leading on into the PC-9800 series (PC-98) the Japanese market produced x86 based non IBM compatible computers.

While these machines may run DOS and Windows, they do not use IBM compatible hardware (The Dos/Windows software are special versions designed to work with the hardware), so games and software from the west will not work on these machines

MsDos calls such as keyboard reading and text writing may work, so a program that only uses MS-Dos functions may work correctly,
however the video hardware is completely different to western machines, with the text and bitmap graphics appearing as separate layers, the Bios calls for keyboard access are also different, so western programs that use the Bios Keyboard access (rather than MS-Dos ones) will not work.

The PC-98 series ranges over more than a decade, with a wide variety of features, but the ones we'll focus on are based on the later models shown below.

	PC9821
Cpu	Various (Up to Pentium)
OS	MS Dos 3-6.2 Windows 3.1 Windows 95 Windows 98 (Special PC98 OS versions required)
Ram	Various (32MB+)
Resolution	640x200 16 color (4096k color palette) 640x400 16 color (4096k color palette) 640x400 256 color (16.7 Million color palette)
Sound	PCM FM add on boards (YM2608)

Resources

PC-9801 Programmers Bible - Best tech manual
PC9800 TechnicalDataBook - HARDWARE 1993 - Not as good, but still very useful
PC-9800 TechnicalDataBook BIOS 1992 - Bios call reference (INTs) Note, these are different to IBM Pc's!
Japanese MS-Dos Handbook - Though dos calls should be the same as western systems

Memory map

20 bit address	Purpose
$0 0000	Ram
$1 0000	Ram
$2 0000	Ram
$3 0000	Ram
$4 0000	Ram
$5 0000	Ram
$6 0000	Ram
$7 0000	Ram
$8 0000
$9 0000
$A 0000	Text Characters (2 bytes per char)
$A 2000	Text Attributes %GRBVUrbs (V=vertline U=Underline r=reverse b=blink s=secret (1=show / 0 = hide))
$A 4000	CG Window 4k
$A 5000
$A 8000	GVRAM0 Plane 0 B
$A BE80	GVRAM0 Plane 1 B
$A FD00
$B 0000	GVRAM1 Plane 0 R
$B 3E80	GVRAM1 Plane 1 R
$B 8000	GVRAM2 Plane 0 G
$B BE80	GVRAM2 Plane 1 G
$B FD00
$C 0000	EMS Memory Window 32k x 4
$D 0000	Kanji Ram
$D 4000	Dictionary Rom
$D 8000	KGC Rom
$D C000
$E 0000	GVRAM3 Plane 0 I
$E 3E80	GVRAM3 Plane 1 I
$E 8000	Bios, Basic Rom 128k
$F 0000	Bios, Basic Rom 128k

Ports

Port	Data	Details
60h	%GGGGGGGG	GDC Parameter
62h	%GGGGGGGG	GDC Command
64h		CRTC Interrupt
68h	%----001T	Monochrome mode (1=Mono 0=Color)
68h	%----010T	Text Resolution (1=320x200 0=640x200)
68h	%----011F	Font (0=6x8 1=7x13)
68h	%----100L	Screen Lines (0=400 1=200)
6Ah	%-------M	Color Mode (0=8 color 1=16 color) (see other 9821 options below)
6Ch	%IGRB0000	Border color RGB Intensity
7Ch	%CR--3210	C=CG mode R=RMW Mode 3210=Plane 3210 enable (1=no 0=yes)
A0h	%GGGGGGGG	GDC Parameter
A2h	%GGGGGGGG	GDC Command
A4h	%-------P	Select Display graphics plane
A6h	%-------P	Select Write graphics plane
A8h	%----PPPP	Select Palette
AAh	%----GGGG	Set palette Green (all 8 bits in 256 col mode)
ACh	%----RRRR	Set palette Red (all 8 bits in 256 col mode)
AEh	%----BBBB	Set palette Blue (all 8 bits in 256 col mode)
&0188 (Varies)	%RRRRRRRR	FM Port 1 Regselect
&018A (Varies)	%DDDDDDDD	FM Port 2 Data

Port 68h Extended options
00h	ATR4 batch call line
01h	ATR4 simple graph
02h	Color Graphics mode
03h	Monocrome graphics mode
04h	80 char mode
05h	40 char mode
06h	Chars 6x8
07h	Chars 7x13
08h	400 line hires
09h	200 lines
0Ah	Code access mode
0Bh	Bitmap mode
0Ch	Disable writing to undefined memory
0Dh	Enable writing to undefined memory
0Eh	Disable screen
0Fh	Enable screen

Port 6Ah Extended options
00h	8 color
01h	16 color
04h	GRCC mode
05h	EGC mode
06h	Extended mode off
07h	Extended mode on
20h	Normal Graphics mode
21h	Extended graphics (256 color)
26h	Normal Display
27h	Full screen reverse
28h	Normal combine
29h	Mathematic combine
2Ah	Normal Palette write
2Bh	Fast Palette write
2Ch	Overscan color off
2Dh	Overscan color on
40h	CRT mode
41h	Plasma display mode
62h	plane format vram
63h	packed pixel vram
68h	Front back plane separate
69h	Front back plane continuous
6Ch	first pixel left
6Dh	first pixel right
84h	GDC 2.5mhz
83h / 85h	GDC 5mhz

GDC Commands (Port 60h / 62h)
Command	Function	Data
%00000000	Reset	8 bytes
%01101011	Start	Show Text
%00001101	Start	Show Text (Alternate ver)
%00001100	Stop	Hide Text
%0111RRRR	Scroll	R=Parameter type
%01001011	CSR Form	Cursor Settings	%C00LLLLL %BBDCCCCC %CCCCCBBB
%01000111	Pitch	Vram width setting	%PPPPPPPP
%01001001	CSRW	Write Cursor p0s	%LLLLLLLL %000HHHHH
%11100000	CSRR	Read Cursor	%LLLLLLLL %000HHHHH %???????? %???????? %????????

INT interrupts

Interrupts	PC-9821	IBM PC (Not this system!)
05h (varies)	Sound
10h		Video
11h		Determine Config
12h		Determine Memory size
13h		Disk
14h		Serial
15h		Cassette (AT)
16h		Keyboard
17h		Parallel
18h	Keyboard / CRT / Graphics	Call ROM Basic
19h	Rs232	Boot Process
1Ah	Printer	Date and Time
1Bh	Hard Disk	Break Key
1Ch	Timer	Periodic Interrupt
1Dh	Graphics	Video Table
1Eh		Drive Table
1Fh		Character Table
20h	MS Dos Terminate	MS Dos Terminate
21h	MS Dos Call	MS Dos Call
22h	Terminate address	Terminate address
23h	Ctrl-C	Ctrl-C
24h	Critical error handler	Critical error handler
25h	Absolute Disk Read	Absolute Disk Read
26h	Absolute Disk Write	Absolute Disk Write
27h	Terminate and stay resident	Terminate and stay resident
2Fh	XMS Memory	Print Spooler
33h	Mouse	Mouse
67h	Memory	EMS
A0h	Graphics LIO Init
A1h	GScreen Graphics mode
A2h	GView
A3h	GColor
A4h	GColor2
A5h	GCLS
A6h	GPset
A7h	Gline
A8h	Gcircle
A9h	Gpaint1
AAh	Gpaint2
ABh	GGET
ACh	GPUT1
ADh	GPUT2
AEh	Groll
AFh	Gpoint
CEh	Gcopy

INT 21 dos calls

INT 21h - Dos calls
00h	End Program
01h	Read Keyboard Input and echo
02h	Print Character
03h	Aux Input
04h	Aux Output
05h	Print to printer
06h	Direct Console I/O
07h	Direct Console Input
08h	Direct Console input - No echo
09h	Print String
0Ah	Buffered keyboard input
0Bh	Keyboard status check
0Ch	Clear keyboard buffer
0Dh	Disk reset
0Eh	Select Drive
0Fh	File open
10h	File Close
11h	Find first directory entry
12h	Find next directory entry
13h	Delete file
14h	Read Sequential
15h	Write Sequential
16h	Create file
17h	Rename file
19h	Get current drive
1Ah	Set Disk transfer address
1Bh	Get Default drive
1Ch	Get Drive Data
21h	Read Random
22h	Write Random
23h	Calculate file size
24h	Set record field
25h	Set Interrupt vector
26h	Create New PSP (Program Segment Prefix)
27h	Read Random Block
28h	Write Random Block
29h	Examine file name
2Ah	Read Date
2Bh	Set Date
2Ch	Read Time
2Dh	Set Time
2Eh	Set Verify Flag
2Fh	Get Disk transfer address
30h	Read DOS Version Number
31h	Terminate and stay resident
33h	Break Check setting
35h	Read Interrupt Vector
36h	Read Free space
38h	Read/Set Country info
39h	Create Subdirectory
3Ah	Delete Subdirectory
3Bh	Change current directory
3Ch	Create a file
3Dh	File Open
3Eh	File Close
3Fh	Read File/Device
40h	Write File/Device
41h	Delete File
42h	Move file pointer
43h	Change File Attributes
44h	Device I/O Control
45h	Copy File Handle
46h	Copy to specified file handle
47h	Read Current Directory
48h	Allocate Memory block
49h	Release Memory block
4Ah	Change Memory block size
4Bh	Load and Execute program
4Ch	End process
4Dh	Read Child process return code
4Eh	Find File
4Fh	Find next File
54h	Read Verify Flag
56h	Move Directory Entry
57h	Read or Set File Date/Time

Keyboard Keycodes

		Top bits
		0-h	1-h	2-h	3-h	4-h	5-h	6-h	7-h
B o t t o m b i t s	-0h	Esc	Q	F	,	-	.	Stop	Shift
	-1h	1	W	G	.	/	Nfer	Copy	Caps
	-2h	2	E	H	/	7	VF1	F1	Kana
	-3h	3	R	J	_	8	VF2	F2	Grph
	-4h	4	T	K	Space	9	VF3	F3	Ctrl
	-5h	5	Y	L	Xfer	*	VF4	F4
	-6h	6	U	;	RlUp	4	VF5	F5
	-7h	7	I	:	RlDn	5		F6
	-8h	8	O	]	Ins	6		F7
	-9h	9	P	Z	Del	+		F8
	-Ah	0	@	X	Up	1		F9
	-Bh	-	[	C	Down	2		F10
	-Ch	^	Enter	V	Left	3
	-Dh	\	A	B	Right	=
	-Eh	Bkspc	S	N	HmClR	0
	-Fh	Tab	D	M	Help	,

Keycode Groups (INT 18h AH=04h)

		Bits
		0	1	2	3	4	5	6	7
K e y c o d e G r o u p	0	Esc	1	2	3	4	5	6	7
	1	8	9	0	-	^	\	Bkspc	Tab
	2	Q	W	E	R	T	Y	U	I
	3	O	P	@	[	Enter	A	Stop	D
	4	F	G	H	J	K	L	+	*
	5	]	Z	X	C	V	B	N	M
	6	,	.	/	_	Space	Xfer	RlUp	RlDn
	7	Ins	Del	Up	Down	Left	Right	HmClr	Help
	8	-	/	7	8	9	*	4	5
	9	6	+	1	2	3	=	0	,
	A	.	Nfer	VF1	VF2	VF3	VF4	VF5
	B							Home
	C	Stop	Copy	F1	F2	F3	F4	F5	F6
	D	F7	F8	F9	F10
	E	Shift	Caps	Kana	Grph	Ctrl

INT 18h calls
AH value	Function	Input	Output
00h	Read key data		AH=Keycode AL=Keydata
01h	Read keybuffer status		AH=Keycode AL=Keydata BH=Bufferstatus (1=data 0=empty)
02h	Inspect shift status		AL=% - - - Ctrl Grph Kana Caps Shift
03h	Reset Keyboard interface status
04h	Inspect Key input status	AL=Keycode Group	AH=Keygroup key status
05h	Read a key from the keybuffer	AH=Keycode	AL=Keydata BX=Status (1=success 0=fail)
06h	Reset buffer
07h	Read Shift Keys + Key data		AH=Keycode AL=Keydata BL=% - - - Ctrl Grph Kana Caps Shift
08h	Inspect Shift Keys + Key data		AH=Keycode AL=Keydata BL=% - - - Ctrl Grph Kana Caps Shift
09h	Create Key data	AL=Keycode BL=Shifts	AH=Keycode AL=Keydata

256 colors mode

In 256 color mode, the VRAM is accessed through two 32k 'windows', one is at A8000h (defined by address E0004h) , the other is at B0000h (defined by address E0006h)

$A 8000	VRAM Window 0 (Defined by E0004h)
$B 0000	VRAM Window 1 (Defined by E0006h)
$B 8000	Unused
$C 0000	EMS Memory Window 32k x 4
$D 0000	Kanji Ram
$D 4000	Dictionary Rom
$D 8000	KGC Rom
$D C000
$E 0000	256 color VRAM selection registers
$E 8000	Bios, Basic Rom 128k
$F 0000	Bios, Basic Rom 128k

Calculating VRAM destination:

VRAM = Yline *640 + Xpixel

BankOffset = A8000h + (VRAM & 7FFFh)
Bank = VRAM >> 15

Write Bank to E0004h
Write Bank+1 to E0006h

24 Bit								16 Bit								8 Bit
7	6	5	4	3	2	1	0	F	E	D	C	B	A	9	8	7	6	5	4	3	2	1	0
-	-	-	-	-	B	B	B	B	O	O	O	O	O	O	O	O	O	O	O	O	O	O	O

256 color bank registers (In ram)
E0004h	Word	VRAM bank window 0 (Bank: 0000-000F)
E0006h	Word	VRAM bank window 1 (Bank: 0000-000F)
E0100h	Byte	Mode (00=Packed pixel 01=Planar)
E0102h	Word	Enable VRAM at F00000h (0000=no 0001=yes)

SSG Registers (AY type)

Register	Meaning	Bit Meaning	Details
0	Tone Pitch L - Channel A (Left)	LLLLLLLL	Lower value = Higher pitch
1	Tone Pitch H - Channel A (Left)	----HHHH	Lower value = Higher pitch
2	Tone Pitch L - Channel B (Center)	LLLLLLLL	Lower value = Higher pitch
3	Tone Pitch H - Channel B (Center)	----HHHH	Lower value = Higher pitch
4	Tone Pitch L - Channel C (Right)	LLLLLLLL	Lower value = Higher pitch
5	Tone Pitch H - Channel C (Right)	----HHHH	Lower value = Higher pitch
6	Noise Generator	---NNNNN	Higher value = Faster noise
7	Mixer + IO	BANNNTTT	N=Noise T=Tone (Channel --CBACBA 1=mute 0=normal) BA=Port B/A direction (1=out 0=in)
8	Amplitude - Channel A (Left)	---EVVVV	E=Envelope (1=Enabled) VVVV=Volume
9	Amplitude - Channel B (Center)	---EVVVV	E=Envelope (1=Enabled) VVVV=Volume
10	Amplitude - Channel C (Right)	---EVVVV	E=Envelope (1=Enabled) VVVV=Volume
11	Envelope L (Volume over time)	LLLLLLLL	Lower value=Faster Envelope
12	Envelope H (Volume over time)	HHHHHHHH	Lower value=Faster Envelope
13	Envelope Selection	----EEEE	Envelope number (See PDF)
14	IO Port A	DDDDDDDD	IO Data port A (joy select)
15	IO Port B	DDDDDDDD	IO Data port B (Joy data)

FM Sound with the YM2608
Get the YM2608 PDF for all the info!

The FM chip uses 2 pairs of ports, ???????? and ???? select the address of the register we want to change, ???? and ????? write the new data, but after each write, we need to check if the FM chip is busy,
To check if the FM chip is busy, read in from port ?????, and check bit 7 - it will return 0 when not busy.

This data is copied from the Genesis

Reg	Purpose	Chn/Op	Bits	Details
$24	Timer A low	ALL	TTTTTTTT	Timer bits 10-2
$25	Timer A high	ALL	------TT	Timer bits 1-0
$26	Timer B	ALL	TTTTTTTT	Timer B
$27	Ch3 CSM Mode & Ch3 Multi-Mode & Enable Timers	ALL	33RROOSS	3= Chn 3 mode / R=timer resets / O= Timer overflows / S = Timer StartStop
$28	Individual Operator Key On/Off	ALL	OOOO-CCC	O=operator (%4321----) / C=Channel (%000=chn 1 %110=chn6)
$29	SCH, IRQ Enable	ALL	S--IIIII	S=Sixchannel / I=IRQ Enable
$2A	DAC Write	ALL	DDDDDDDD	D=Data
$2B	DAC Enable	ALL	E-------	E=enable
$30	Multiplier & Detune	Ch1 Op1	-DDDMMMM	D=Detune / M=Multiplier
$31	Multiplier & Detune	Ch2 Op1	-DDDMMMM	D=Detune / M=Multiplier
$32	Multiplier & Detune	Ch3 Op1	-DDDMMMM	D=Detune / M=Multiplier
$34	Multiplier & Detune	Ch1 Op2	-DDDMMMM	D=Detune / M=Multiplier
$35	Multiplier & Detune	Ch2 Op2	-DDDMMMM	D=Detune / M=Multiplier
$36	Multiplier & Detune	Ch3 Op2	-DDDMMMM	D=Detune / M=Multiplier
$38	Multiplier & Detune	Ch1 Op3	-DDDMMMM	D=Detune / M=Multiplier
$39	Multiplier & Detune	Ch2 Op3	-DDDMMMM	D=Detune / M=Multiplier
$3A	Multiplier & Detune	Ch3 Op3	-DDDMMMM	D=Detune / M=Multiplier
$3C	Multiplier & Detune	Ch1 Op4	-DDDMMMM	D=Detune / M=Multiplier
$3D	Multiplier & Detune	Ch2 Op4	-DDDMMMM	D=Detune / M=Multiplier
$3E	Multiplier & Detune	Ch3 Op4	-DDDMMMM	D=Detune / M=Multiplier
$40	Total Level	Ch1 Op1	-TTTTTTT	T=Total Level (0=largest)
$41	Total Level	Ch2 Op1	-TTTTTTT	T=Total Level (0=largest)
$42	Total Level	Ch3 Op1	-TTTTTTT	T=Total Level (0=largest)
$44	Total Level	Ch1 Op2	-TTTTTTT	T=Total Level (0=largest)
$45	Total Level	Ch2 Op2	-TTTTTTT	T=Total Level (0=largest)
$46	Total Level	Ch3 Op2	-TTTTTTT	T=Total Level (0=largest)
$48	Total Level	Ch1 Op3	-TTTTTTT	T=Total Level (0=largest)
$49	Total Level	Ch2 Op3	-TTTTTTT	T=Total Level (0=largest)
$4A	Total Level	Ch3 Op3	-TTTTTTT	T=Total Level (0=largest)
$4C	Total Level	Ch1 Op4	-TTTTTTT	T=Total Level (0=largest)
$4D	Total Level	Ch2 Op4	-TTTTTTT	T=Total Level (0=largest)
$4E	Total Level	Ch3 Op4	-TTTTTTT	T=Total Level (0=largest)
$50	Attack Rate & Rate Key Scaling	Ch1 Op1	RR-AAAAA	R=Rate Scaling / A = Attack rate
$51	Attack Rate & Rate Key Scaling	Ch2 Op1	RR-AAAAA	R=Rate Scaling / A = Attack rate
$52	Attack Rate & Rate Key Scaling	Ch3 Op1	RR-AAAAA	R=Rate Scaling / A = Attack rate
$54	Attack Rate & Rate Key Scaling	Ch1 Op2	RR-AAAAA	R=Rate Scaling / A = Attack rate
$55	Attack Rate & Rate Key Scaling	Ch2 Op2	RR-AAAAA	R=Rate Scaling / A = Attack rate
$56	Attack Rate & Rate Key Scaling	Ch3 Op2	RR-AAAAA	R=Rate Scaling / A = Attack rate
$58	Attack Rate & Rate Key Scaling	Ch1 Op3	RR-AAAAA	R=Rate Scaling / A = Attack rate
$59	Attack Rate & Rate Key Scaling	Ch2 Op3	RR-AAAAA	R=Rate Scaling / A = Attack rate
$5A	Attack Rate & Rate Key Scaling	Ch3 Op3	RR-AAAAA	R=Rate Scaling / A = Attack rate
$5C	Attack Rate & Rate Key Scaling	Ch1 Op4	RR-AAAAA	R=Rate Scaling / A = Attack rate
$5D	Attack Rate & Rate Key Scaling	Ch2 Op4	RR-AAAAA	R=Rate Scaling / A = Attack rate
$5E	Attack Rate & Rate Key Scaling	Ch3 Op4	RR-AAAAA	R=Rate Scaling / A = Attack rate
$60	Decay Rate & AM Enable	Ch1 Op1	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$61	Decay Rate & AM Enable	Ch2 Op1	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$62	Decay Rate & AM Enable	Ch3 Op1	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$64	Decay Rate & AM Enable	Ch1 Op2	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$65	Decay Rate & AM Enable	Ch2 Op2	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$66	Decay Rate & AM Enable	Ch3 Op2	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$68	Decay Rate & AM Enable	Ch1 Op3	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$69	Decay Rate & AM Enable	Ch2 Op3	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$6A	Decay Rate & AM Enable	Ch3 Op3	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$6C	Decay Rate & AM Enable	Ch1 Op4	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$6D	Decay Rate & AM Enable	Ch2 Op4	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$6E	Decay Rate & AM Enable	Ch3 Op4	A--DDDDD	A=Amplitude Mod Enable / D= Decay rate
$70	Sustain Rate	Ch1 Op1	---SSSSS	S=Sustain Rate
$71	Sustain Rate	Ch2 Op1	---SSSSS	S=Sustain Rate
$72	Sustain Rate	Ch3 Op1	---SSSSS	S=Sustain Rate
$74	Sustain Rate	Ch1 Op2	---SSSSS	S=Sustain Rate
$75	Sustain Rate	Ch2 Op2	---SSSSS	S=Sustain Rate
$76	Sustain Rate	Ch3 Op2	---SSSSS	S=Sustain Rate
$78	Sustain Rate	Ch1 Op3	---SSSSS	S=Sustain Rate
$79	Sustain Rate	Ch2 Op3	---SSSSS	S=Sustain Rate
$7A	Sustain Rate	Ch3 Op3	---SSSSS	S=Sustain Rate
$7C	Sustain Rate	Ch1 Op4	---SSSSS	S=Sustain Rate
$7D	Sustain Rate	Ch2 Op4	---SSSSS	S=Sustain Rate
$7E	Sustain Rate	Ch3 Op4	---SSSSS	S=Sustain Rate
$80	Release Rate & Sustain Level	Ch1 Op1	SSSSRRRR	S=Sustain Level / Release Rate
$81	Release Rate & Sustain Level	Ch2 Op1	SSSSRRRR	S=Sustain Level / Release Rate
$82	Release Rate & Sustain Level	Ch3 Op1	SSSSRRRR	S=Sustain Level / Release Rate
$84	Release Rate & Sustain Level	Ch1 Op2	SSSSRRRR	S=Sustain Level / Release Rate
$85	Release Rate & Sustain Level	Ch2 Op2	SSSSRRRR	S=Sustain Level / Release Rate
$86	Release Rate & Sustain Level	Ch3 Op2	SSSSRRRR	S=Sustain Level / Release Rate
$88	Release Rate & Sustain Level	Ch1 Op3	SSSSRRRR	S=Sustain Level / Release Rate
$89	Release Rate & Sustain Level	Ch2 Op3	SSSSRRRR	S=Sustain Level / Release Rate
$8A	Release Rate & Sustain Level	Ch3 Op3	SSSSRRRR	S=Sustain Level / Release Rate
$8C	Release Rate & Sustain Level	Ch1 Op4	SSSSRRRR	S=Sustain Level / Release Rate
$8D	Release Rate & Sustain Level	Ch2 Op4	SSSSRRRR	S=Sustain Level / Release Rate
$8E	Release Rate & Sustain Level	Ch3 Op4	SSSSRRRR	S=Sustain Level / Release Rate
$90	SSG-Envelope Generator	Ch1 Op1	----EEEE	E=Envelope Gen
$91	SSG-Envelope Generator	Ch2 Op1	----EEEE	E=Envelope Gen
$92	SSG-Envelope Generator	Ch3 Op1	----EEEE	E=Envelope Gen
$94	SSG-Envelope Generator	Ch1 Op2	----EEEE	E=Envelope Gen
$95	SSG-Envelope Generator	Ch2 Op2	----EEEE	E=Envelope Gen
$96	SSG-Envelope Generator	Ch3 Op2	----EEEE	E=Envelope Gen
$98	SSG-Envelope Generator	Ch1 Op3	----EEEE	E=Envelope Gen
$99	SSG-Envelope Generator	Ch2 Op3	----EEEE	E=Envelope Gen
$9A	SSG-Envelope Generator	Ch3 Op3	----EEEE	E=Envelope Gen
$9C	SSG-Envelope Generator	Ch1 Op4	----EEEE	E=Envelope Gen
$9D	SSG-Envelope Generator	Ch2 Op4	----EEEE	E=Envelope Gen
$9E	SSG-Envelope Generator	Ch3 Op4	----EEEE	E=Envelope Gen
$A0	Frequency low (Write Second)	Ch1	PPPPPPPP	P=Frequency Position L
$A1	Frequency low (Write Second)	Ch2	PPPPPPPP	P=Frequency Position L
$A2	Frequency low (Write Second)	Ch3	PPPPPPPP	P=Frequency Position L
$A4	Frequency high & Octave (Write first)	Ch1	--OOOPPP	O=Octive / P=Position H
$A5	Frequency high & Octave (Write first)	Ch2	--OOOPPP	O=Octive / P=Position H
$A6	Frequency high & Octave (Write first)	Ch3	--OOOPPP	O=Octive / P=Position H
$A8	Frequency low during Multi-Mode	Ch3 Op2	PPPPPPPP	P=Frequency Position L
$A9	Frequency low during Multi-Mode	Ch3 Op3	PPPPPPPP	P=Frequency Position L
$AA	Frequency low during Multi-Mode	Ch3 Op4	PPPPPPPP	P=Frequency Position L
$AC	Frequency high & Octave during Multi-Mode	Ch3 Op2	--OOOPPP	O=Octive / P=Position H
$AD	Frequency high & Octave during Multi-Mode	Ch3 Op3	--OOOPPP	O=Octive / P=Position H
$AE	Frequency high & Octave during Multi-Mode	Ch3 Op4	--OOOPPP	O=Octive / P=Position H
$B0	Algorithm & Feedback	Ch1	--FFFAAA	F=Feedback / A=Algorithm
$B1	Algorithm & Feedback	Ch2	--FFFAAA	F=Feedback / A=Algorithm
$B2	Algorithm & Feedback	Ch3	--FFFAAA	F=Feedback / A=Algorithm

FM Algorithm (&B1/B2)
The algorithm number is one of 8 - each one defines how the different operations build up to build a sound:

Sound Ops

FM Sound over time
The sound created is affected over time by the various registers, we can see a simple representation below:

Sound Over Time

NEC PC9821 V13

I recently purchased a cheap PC-9821 V13, which worked great, but came without hard-drive, so I had to figure out how to get it set up and work out what it could do! Here I'll document my findings for anyone else who may have the same issues / questions

Note, As these machines are Japanese, you'll have to use Japanese Dos/Windows with them, as western versions will not support the custom hardware.

Useful Resources

nw150doswin98 - A disk image with Dos Windows pre-installed. I flashed this to a 2GB CF2 card, and used it with a PATA converter as my main hard drive. It worked great, though I re-installed Windows 98 to get the drivers working easily (Windows installer included in image)
PC98 Wikipedia article - More details on the PC98
TGP-VR4 - Drivers for the 3D card the machine came with, I had a hell of a time finding these, so I uploaded them here!

DOS!

Dos works fine, The machine uses MSDOS 6.2, but although it looks like regular dos, normal (western) dos apps almost certainly won't work - even MS-DOS EDIT is missing!

I tried an old XT game 'RearGard' - The graphics appeared corrupted, and as a second layer over the text! It seems the 'CGA' vram is in the same address range as the PC98 VRAM, however it's clearly in a completely different incompatible format, and it seems the text / graphics screens are different layers! Also the game seems to have crashed... which happens to most western dos stuff!

Amusingly ELIZA seems to work fine! I assume this is because it's text input / screen output is all done via DOS calls, not accessing hardware directly.

Western games aside, I tried some of the pre-installed Japanese games on the hard drive image, and I didn't have much luck there either! I saw a lot of graphical issues, and the PC-88 version of Xenon 2 instantly crashed!

Windows!

Results on Windows were very different to DOS! Whereas dos was pretty much useless on this machine for my western games, Windows worked very well! I tried out some of my old games on the machine!

I was able to install 'Virtua Cop' - it worked fine (bit slow on the P133 cpu), I was impressed that my western copy's setup routine seemed to support Japanese, and even came with the PC98 Directx install!!

Die hard Trilogy also seemed to install and work ok, though it's slow and refused to support my 3D accelerator (even though DirectX recognized it)

The Windows Version of 'The 7th guest' worked, though while speech worked, there was no music. That's no surprise as the internal sound card does not have FM synthesis, it's PCM only!
The Windows Version of 'The 11th hour' did not work, It complained I had no 'XMIDI' sound, and refused to load.

Black Dahlia installed fine, and worked well, but it seems to access the keyboard directly via hardware keycodes, as the keys pressed did not appear in game as I expected. I had to practice with save game names to figure out how to use the keyboard when needed in games.

Leisure Suit Larry 7 (Love for Sail) - Installed fine, but Windows95 version crashed, Windows 3.1 version worked fine (didn't have any keyshift problems either)... I didn't try the Dos version, as it would have certainly crashed!... How amazing is this game to have different versions supporting THREE operating systems!

Key shifts

The hardware key codes do not match a western keyboard, but I was able to play Blach dahlia fine once I knew the 'shifts' I had to make to compensate for the difference.

Numbers row, shifted 1 key right (2 presses 1 .... 1 presses esc)
Q row, Shifted 0 keys right (Q presses Q)
A row, Shifted 1 keys right (S presses A)
Z row, Shifted 3 keys right (V presses Z)
Space presses .
Del presses Space

Screenshots

The boot screen!	RearGard Graphics are corrupt! The VRAM is at a similar address, but the format is totally different. Notice the Text/Graphics are separate layers.
Western Eliza works fine! This is because it's Text+Keys only, and using MS-DOS calls This game was copied from my old PC1512 back in the 80s!	Even the Japanese games are struggling! Some interlacing/ screen mode problem!
Japanese Windows 98 works well, and many western games work fine, though my machine has no FM/MIDI card. Note, first HDD is A:, and floppy is C: !!