Programmer's Guide to Yamaha YMF 262/OPL3 FM Music Synthesizer

HTML Version 1.12 Last Updated Nov-23-2000
(based on plaintext Version 1.00 Nov-24-1994)
Written by Vladimir Arnost, QA-Software
e-mail: arnost@dcse.fee.vutbr.cz


This manual can be distributed freely if not modified.

Disclaimer

I assume no responsibility for any damages arising out of use or inability to use this text. No warranty is provided about correctness of any information in this file. You are on your own.

Table of Contents

• Introduction
  
• Description of the Synthesizer
  • Some basic facts
  • Synthesis modes
  
  
• Programming the Synthesizer
• Register Map
  • Examples
  
  
• OPL3 Register Reference
  • Status Register
  • Data Registers
    • 01: Test Register / Waveform Select Enable
    • 02: Timer 1 Count
    • 03: Timer 2 Count
    • 004: IRQ-Reset / Mask / Start
    • 104: Four-Operator Enable
    • 105: OPL3 Mode Enable
    • 08: CSW / NOTE-SEL
    • 20-35: Tremolo / Vibrato / Sustain / KSR / Frequency Multiplication Factor
    • 40-55: Key Scale Level / Output Level
    • 60-75: Attack Rate / Decay Rate
    • 80-95: Sustain Level / Release Rate
    • A0-A8: Frequency Number
    • B0-B8: Key On / Block Number / F-Number(hi bits)
    • BD: Tremolo Depth / Vibrato Depth / Percussion Mode / BD/SD/TT/CY/HH On
    • C0-C8: FeedBack Modulation Factor / Synthesis Type
    • E0-F5: Waveform Select
  
  
• Appendixes
  • Examples
  • Detection Methods
  
  
• References

1. Introduction

The chip I am going to describe is getting more and more common, but programming information is still scarce, so I have decided to fill in this gap. All information contained in this file is a result of my experience in Adlib programming, research (read: reverse engineering) and finally of my effort to write down everything necessary to understand and use this piece of hardware. No official sources (i.e. development kits, books about this topic, etc.) were available to me except:

• Adlib Programming Guide - by Tero Totto, and
• The PC Games Programmers Encyclopedia V1.0

As far as I know, there are four major sound cards based on OPL3 chip:

• Sound Blaster Pro II (not Sound Blaster Pro I) and many clones
• Sound Blaster 16 and AWE32
• Adlib Gold
• Pro Audio Spectrum Plus/16

Note: I assume some knowledge of FM music programming (mainly Adlib FM synthesizer) in this manual. If you are new to this topic I recommend you try Adlib first before going higher. Anyway, OPL3 is a direct descendant of OPL2 (what a surprise), so most features of OPL2 are also present on OPL3.

2. Description of the Synthesizer

2.1 Some basic facts

My card's user manual says: "[this card contains] ... a stereo music FM synthesizer with 20 channels consisting of four (4) operators each ... ". I thought: "Wow -- that's together eighty operators. This must be a GOOD sound-card." I was wrong. Just another advertising lie.

So let's clear some facts. First, OPL3 has only thirty-six (36) operators which can be combined in several ways:

• 18 FM channels (36 operators), or
• 15 FM channels (30 ops) and 5 percussion instruments (6 ops), giving us 20 channels altogether, or
• up to 6 four-operator FM channels (max 24 ops), the rest again being divided into two-operator FM channels and drums.

2.2 Synthesis modes

1. Two-operator Additive Synthesis

   Output of both operators is simply added. It is the simplest way to make any sound, and it works on both OPL2 and OPL3. The diagram should make it clear.
   

   	+------------+
   	|            |
   	| Operator 1 +--------+
   	|            |        |
   	+------------+        |
   			      +--------> Output
   	+------------+        |
   	|            |        |
   	| Operator 2 +--------+
   	|            |
   	+------------+
   

2. Two-operator Frequency Modulation (FM) Synthesis

   Output from the first operator (Modulator) is sent to the input of the second one (Carrier) and is used to modulate (alter) frequency of the second operator. Only the second operator produces sound. Most of interesting sounds are made this way. This also works on OPL2. Hope the picture helps.

   	+------------+         +------------+
   	|            |         |            |
   	| Operator 1 +-------->| Operator 2 +--------> Output
   	|(Modulator) |         | (Carrier)  |
   	+------------+         +------------+
   

3. Four-operator "Mess" Modulation Synthesis

   All of OPL3's 4-OP configurations are combinations of the above two modes of synthesis. OPL3 combines these two modes in four ways. I have no words to describe these four ways. Only the pictures can show their principle.

   1. FM-FM Mode

      	+-------+      +-------+      +-------+      +-------+
      	|       |      |       |      |       |      |       |
      	| Op. 1 +----->| Op. 2 +----->| Op. 3 +----->| Op. 4 +-----> Output
      	|       |      |       |      |       |      |       |
      	+-------+      +-------+      +-------+      +-------+
      

   2. AM-FM Mode

      	+-------+
      	|       |
      	| Op. 1 +-----------------------------------+
      	|       |                                   |
      	+-------+                                   |
      						    |
      	+-------+      +-------+      +-------+     |
      	|       |      |       |      |       |     |
      	| Op. 2 +----->| Op. 3 +----->| Op. 4 +-----+-----> Output
      	|       |      |       |      |       |
      	+-------+      +-------+      +-------+
      

   3. FM-AM Mode

      	+-------+      +-------+
      	|       |      |       |
      	| Op. 1 +----->| Op. 2 +-----+
      	|       |      |       |     |
      	+-------+      +-------+     |
      				     +-----> Output
      	+-------+      +-------+     |
      	|       |      |       |     |
      	| Op. 3 +----->| Op. 4 +-----+
      	|       |      |       |
      	+-------+      +-------+
      

   4. AM-AM Mode

      	+-------+
      	|       |
      	| Op. 1 +--------------------+
      	|       |                    |
      	+-------+                    |
      				     |
      	+-------+      +-------+     |
      	|       |      |       |     |
      	| Op. 2 +----->| Op. 3 +-----+-----> Output
      	|       |      |       |     |
      	+-------+      +-------+     |
      				     |
      	+-------+                    |
      	|       |                    |
      	| Op. 4 +--------------------+
      	|       |
      	+-------+
      

   Nice, aren't they?
   
   The only way I think this can be written is a math formula. Symbol + (plus) means additive synthesis, and * (asterisk) means frequency modulation (Op1 * Op2 means operator 1 modulates operator 2, not vice versa). Here they are:
   

   FM-FM Mode: AM-FM Mode: FM-AM Mode: AM-AM Mode:

   (Op1 * Op2 * Op3 * Op4) ----> Output Op1 + (Op2 * Op3 * Op4) ----> Output (Op1 * Op2) + (Op3 * Op4) --> Output Op1 + (Op2 * Op3) + Op4 ----> Output

   
   

   Note 1: Actually, modes FM-AM and AM-AM are redundant, because they can be replaced by any pair of 2-OP channels operating at the same frequency.
   In FM-AM mode, the operator assignment would be straightforward: (Op1, Op2) and (Op3, Op4), both running in FM mode.
   In the case of AM-AM Mode, a small rearrangement of operators would be necessary: (Op1, Op4) in AM mode and (Op2, Op3) in FM mode.
   
   Note 2: This document uses AM as a shorthand form of Additive Synthesis. Actually this is not any kind of modulation, just a simple addition of two signals. The AM shorthand was chosen as an "obvious" opposite of FM (as seen on your radio receiver). Please note that the OPL2/3 chips are unable to automatically perform any kind Amplitude Modulation other than tremolo effect.
   

4. Percussion Mode

   In this mode 6 operators are used to produce five different percussion instruments:

   • Bass Drum (2 operators)
   • Snare Drum (1 operator)
   • Tom-Tom (1 operator)
   • Cymbal (1 operator)
   • Hi-Hat (1 operator)

   Because these instruments occupy only three melodic channels, only Bass Drum, Snare Drum and Tom-Tom frequencies can be set. Cymbal and Hi-Hat frequencies are fixed.

   This mode is identical with that of OPL2. For more details see ADLIB.DOC.

3. Programming the Synthesizer

OPL3 may be found at the following addresses:

OPL3 Base Port Assignment
220h or 240h (selectable) and 388h	Sound Blaster Pro II, 16, 32, AWE32/64 and Live, ESS 688, etc.
388h	Adlib Gold, Windows Sound System
388h ?	Pro Audio Spectrum Plus/16 (could anyone provide some more info?)

The base address of the synthesizer will be called "base".

The chip occupies four I/O addresses:

base+0	Primary index register (write), Status register (read)
base+1	Primary data register (write-only)
base+2	Secondary index register (write)
base+3	Secondary data register (write-only)

The index registers are used to select internal registers and data registers are used to write to them. Status register returns the state of two timers built in the chip. OPL3 contains two sets of registers. The Primary set maps to channels 0-8 (operators 0-17) and the secondary maps to channels 9-17 (operators 18-35). The reason for this is simple: all these registers wouldn't fit into single register set.

Unlike Adlib (OPL2), OPL3 doesn't need delay between register writes. With OPL2 you had to wait 3.3 us after index register write and another 23 us after data register write. On the contrary OPL3 doesn't need (almost) any delay after index register write and only 0.28 us after data register write. This means you can neglect the delays and considerably speed up your music driver. But using reasonable delays will certainly do no harm.

The data registers can't be read (they are write-only) on both OPL2 and OPL3.

4. Register Map

The registers are grouped in the same manner as in the OPL2 chip. Programs using both OPL2 and OPL3 chips may use the same code provided that their direct I/O interface is well written. The only thing you have to change is operator-to-register mapping, which must accomodate the fact that registers are spread between two register sets.

(The register map is nearly the same so I dared to copy it from ADLIB.DOC.)

Status Register (base+0):

Empty fields are considered reserved and should not be used or relied upon their value.

Data Registers (base+1, base+3):

Notes:
*	This register exists only at port base+1
**	This register exists only at port base+3

For register bases A0, B0 and C0 there is one register per output channel. The primary register set holds the first nine channels (0-8) and the secondary holds last nine channels (9-17).

For bases 20, 40, 60, 80 and E0 there are two registers per channel. Each register maps to one operator. Unfortunately the operator's register numbers are not continuous. The following table shows which operator maps to which register set and offset (in hex).

The following tables summarize which operators form a channel in various modes:

1. Two-operator Melodic Mode

+------------+--------------------------------------------------------------+
| Channel    | 0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17 |
+------------+--------------------------------------------------------------+
| Operator 1 | 0  1  2  6  7  8  12 13 14 18 19  20  24  25  26  30  31  32 |
| Operator 2 | 3  4  5  9  10 11 15 16 17 21 22  23  27  28  29  33  34  35 |
+------------+--------------------------------------------------------------+

2. Two-operator Melodic and Percussion Mode

+------------+--------------------------------------------------------------+
| Channel    | 0  1  2  3  4  5  BD SD TT CY HH  9  10 11 12 13 14 15 16 17 |
+------------+--------------------------------------------------------------+
| Operator 1 | 0  1  2  6  7  8  12 16 14 17 13  18 19 20 24 25 26 30 31 32 |
| Operator 2 | 3  4  5  9  10 11 15              21 22 23 27 28 29 33 34 35 |
+------------+--------------------------------------------------------------+

3. Four-operator Melodic Mode

+------------+---------------------------------------------------+
| Channel    | 0   1   2    6   7   8    9   10  11   15  16  17 |
+------------+---------------------------------------------------+
| Operator 1 | 0   1   2    12  13  14   18  19  20   30  31  32 |
| Operator 2 | 3   4   5    15  16  17   21  22  23   33  34  35 |
| Operator 3 | 6   7   8                 24  25  26              |
| Operator 4 | 9   10  11                27  28  29              |
+------------+---------------------------------------------------+

Channels 3, 4, 5 and 12, 13, 14 can't be used separately because their operators became part of channels 0, 1, 2 and 9, 10, 11 respectively. For instance a four-operator channel 1 consists of two two-operator channels number 1 and 4. (The second 2-OP channel number is always the first 2-OP channel number plus three.)

OPL3 allows you to enable/disable 4-OP mode separately for any of channels 0, 1, 2, 9, 10 and 11 (see register 104h in the reference below). This means for instance when you switch only channel 2 into 4-OP mode, channels number 0, 1, 3, 4, 6, 7, 8, 9, etc. will be still independent 2-OP channels.

Channels 6, 7, 8 and 15, 16, 17 are always two-operator ones. They can't be grouped to form four-operator channels.

4. Four-operator Melodic and Percussion Mode

+------------+--------------------------------------------------------+
| Channel    | 0   1   2    BD SD TT CY HH    9   10  11   15  16  17 |
+------------+--------------------------------------------------------+
| Operator 1 | 0   1   2    12 16 14 17 13    18  19  20   30  31  32 |
| Operator 2 | 3   4   5    15                21  22  23   33  34  35 |
| Operator 3 | 6   7   8                      24  25  26              |
| Operator 4 | 9   10  11                     27  28  29              |
+------------+--------------------------------------------------------+

Examples

• Two-operator channel #14 consists of operators 26 and 29 which occupy these registers (all are in the secondary register set):

  	12A - Operator 1 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	12D - Operator 2 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	14A - Operator 1 - Key Scale Level/Output Level
  	14D - Operator 2 - Key Scale Level/Output Level
  	16A - Operator 1 - Attack Rate/Decay Rate
  	16D - Operator 2 - Attack Rate/Decay Rate
  	18A - Operator 1 - Sustain Level/Release Rate
  	18D - Operator 2 - Sustain Level/Release Rate
  	1A5 -              Frequency Number (low)
  	1B5 -              Key On/Block Number/Frequency Number (high)
  	1C5 -              FeedBack/Synthesis Type
  	1EA - Operator 1 - Waveform Select
  	1ED - Operator 2 - Waveform Select
  

• Four-operator channel #1 consists of operators 1, 4, 7 and 10. All registers except register 104h are in the primary set:

  	104 - bit 1 = 1  - Enable Four-Operator Synthesis in channel #1
  	 21 - Operator 1 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	 24 - Operator 2 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	 29 - Operator 3 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	 2C - Operator 4 - Tremolo/Vibrato/Sustain/KSR/Multiplication
  	 41 - Operator 1 - Key Scale Level/Output Level
  	 44 - Operator 2 - Key Scale Level/Output Level
  	 49 - Operator 3 - Key Scale Level/Output Level
  	 4C - Operator 4 - Key Scale Level/Output Level
  	 61 - Operator 1 - Attack Rate/Decay Rate
  	 64 - Operator 2 - Attack Rate/Decay Rate
  	 69 - Operator 3 - Attack Rate/Decay Rate
  	 6C - Operator 4 - Attack Rate/Decay Rate
  	 81 - Operator 1 - Sustain Level/Release Rate
  	 84 - Operator 2 - Sustain Level/Release Rate
  	 89 - Operator 3 - Sustain Level/Release Rate
  	 8C - Operator 4 - Sustain Level/Release Rate
  	 A1 -              Frequency Number (low)
  	 A4 -              Unused
  	 B1 -              Key On/Block Number/Frequency Number (high)
  	 B4 -              Unused
  	 C1 -              FeedBack/Synthesis Type (part 1)
  	 C4 -              Synthesis Type (part 2)
  	 E1 - Operator 1 - Waveform Select
  	 E4 - Operator 2 - Waveform Select
  	 E9 - Operator 3 - Waveform Select
  	 EC - Operator 4 - Waveform Select
  

Note: If a register number is greater than 100h, then it belongs into the secondary register set. (I use this numbering to emphasize the fact that the particular register MUST be written to the secondary set.) See Appendix A.

5. OPL3 Register Reference

Because the registers of OPL3 are almost the same as of OPL2, I have copied their descriptions from file ADLIB.DOC.

5.1 Status Register:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |IRQ|T1 |T2 |     Not used      |
   +---+---+---+---+---+---+---+---+

Timer interrupts are not wired to any IRQ (why??). The timers can be used to detect the OPL2/OPL3 chip (see Appendix B).

5.2 Data Registers:

01: Test Register / Waveform Select Enable:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |       |WSE|   Test Register   |
   +---+---+---+---+---+---+---+---+

02: Timer 1 Count:

Upward 8 bit counter with a resolution of 80 usec. If an overflow occurs, the status register bit is set, and the preset value is loaded into the timer again.

03: Timer 2 Count:

Same as Timer 1, but with a resolution of 320 usec.

004 (port: base+1): IRQ-Reset / Mask / Start:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |Rst|T1M|T2M|           |T2S|T1S|
   +---+---+---+---+---+---+---+---+

104 (port: base+3): Four-Operator Enable:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |       |ChB|ChA|Ch9|Ch2|Ch1|Ch0|
   +---+---+---+---+---+---+---+---+

If reset to zero, OPL3 can produce 18 two-operator sounds at a time.
If nonzero, OPL3 produces four-operator sound in appropriate channel pair.

105 (port: base+3): OPL3 Mode Enable:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |                           |OPL|
   +---+---+---+---+---+---+---+---+

08: CSW / NOTE-SEL:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |CSW|N-S|                       |
   +---+---+---+---+---+---+---+---+

20-35: Tremolo / Vibrato / Sustain / KSR / Frequency Multiplication Factor:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |Tre|Vib|Sus|KSR| Multiplication|
   +---+---+---+---+---+---+---+---+

		+-------+--------+
		| MULTI | Factor |
		+-------+--------+
		|   0   |   1/2  |
		|   1   |    1   |
		|   2   |    2   |
		|   3   |    3   |
		|   4   |    4   |
		|   5   |    5   |
		|   6   |    6   |
		|   7   |    7   |
		|   8   |    8   |
		|   9   |    9   |
		|  10   |   10   |
		|  11   |   10   |
		|  12   |   12   |
		|  13   |   12   |
		|  14   |   15   |
		|  15   |   15   |
		+-------+--------+

40-55: Key Scale Level / Output Level:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |  KSL  |      Output Level     |
   +---+---+---+---+---+---+---+---+

		+-----+-------------+
		| KSL | Attenuation |
		+-----+-------------+
		|  0  | -           |
		|  1  | 1.5 dB/oct  |
		|  2  | 3.0 dB/oct  |
		|  3  | 6.0 dB/oct  |
		+-----+-------------+

		+-------+------+------+------+------+
		| Mode  | Op 1 | Op 2 | Op 3 | Op 4 |
		+-------+------+------+------+------+
		|  AM   |  +   |  +   | N/A  | N/A  |
		|  FM   |  -   |  +   | N/A  | N/A  |
		| FM-FM |  -   |  -   |  -   |  +   |
		| AM-FM |  +   |  -   |  -   |  +   |
		| FM-AM |  -   |  +   |  -   |  +   |
		| AM-AM |  +   |  -   |  +   |  +   |
		+-------+------+------+------+------+

60-75: Attack Rate / Decay Rate:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |  Attack Rate  |  Decay Rate   |
   +---+---+---+---+---+---+---+---+

80-95: Sustain Level / Release Rate:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   | Sustain Level |  Release Rate |
   +---+---+---+---+---+---+---+---+

A0-A8: Frequency Number:

B0-B8: Key On / Block Number / F-Number(hi bits):

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |       |KEY| Block Num.| Freq  |
   +---+---+---+---+---+---+---+---+

F-Number = Music Frequency * 2^(20-Block) / 49716 Hz

Note: In four-operator mode only the register value of Operators 1 and 2 is used, value of Operators 3 and 4 in this register is ignored. In other words: one channel uses only one frequency, block and KEY-ON value at a time, regardless whether it is a two- or four-operator channel.

BD: Tremolo Depth / Vibrato Depth / Percussion Mode / BD/SD/TT/CY/HH On:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |Tre|Vib|Per|BD |SD |TT |CY |HH |
   +---+---+---+---+---+---+---+---+

C0-C8: FeedBack Modulation Factor / Synthesis Type:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |       | R | L | FeedBack  |Syn|
   +---+---+---+---+---+---+---+---+

		+----------+--------+
		| FeedBack | Factor |
		+----------+--------+
		|    0     |   0    |
		|    1     |  n/16  |
		|    2     |  n/8   |
		|    3     |  n/4   |
		|    4     |  n/2   |
		|    5     |   n    |
		|    6     |  2.n   |
		|    7     |  4.n   |
		+----------+--------+

		+--------+--------+--------+
		| Op 1&2 | Op 3&4 |  Type  |
		+--------+--------+--------+
		|    0   |  NONE  |   FM   |
		|    1   |  NONE  |   AM   |
		|    0   |    0   | FM-FM  |
		|    1   |    0   | AM-FM  |
		|    0   |    1   | FM-AM  |
		|    1   |    1   | AM-AM  |
		+--------+--------+--------+

E0-F5: Waveform Select:

   +-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
   |                   | WaveForm  |
   +---+---+---+---+---+---+---+---+

bits 0-2: WaveForm Select (WS):

WaveForm 0: Sine WaveForm 1: Half-Sine WaveForm 2: Abs-Sine WaveForm 3: Pulse-Sine

WaveForm 4: Sine - even periods only WaveForm 5: Abs-Sine - even periods only WaveForm 6: Square WaveForm 7: Derived Square

Note: Bit 5 of register 01 must be set to use waveforms other than sine. Waveforms 4-7 are available only on OPL3.

Appendixes

Appendix A - Examples

These examples show a few working routines used in my MUS Player. They are written in Borland C++ 3.1 but should be easy to translate to any other language.

--------------------------------- cut here ---------------------------------
// I prefer using these Assembler-like types
typedef unsigned int  WORD;
typedef unsigned char BYTE;

/*
 * FM Synthesizer base port. SB Pro II - 0x220, Adlib 0x388
 */
WORD FMport = 0x220;

/*
 * Enables OPL3 extensions.
 */
WORD OPL3 = 1;

/*
 * Direct write to any Adlib/SB Pro II FM synthetiser register.
 *   reg - register number (range 0x001-0x0F5 and 0x101-0x1F5). When high byte
 *         of reg is zero, data go to port FMport, otherwise to FMport+2
 *   data - register value to be written
 */
BYTE FMwriteReg(WORD reg, BYTE data)
{
    asm {
	mov	dx,FMport
	mov	ax,reg
	or	ah,ah		// high byte is nonzero -- write to port base+2
	jz	out1
	inc	dx
	inc	dx
    }
out1: asm {
	out	dx,al
	mov	cx,6
    }
loop1:asm {			// delay between writes
	in	al,dx
	loop	loop1

	inc	dx
	mov	al,data
	out	dx,al
	dec	dx
	mov	cx,36
    }
loop2:asm {			// delay after data write
	in	al,dx
	loop	loop2
    }
    return _AL;
}

/*
 * Write to an operator pair. To be used for register bases of 0x20, 0x40,
 * 0x60, 0x80 and 0xE0.
 */
void FMwriteChannel(BYTE regbase, BYTE channel, BYTE data1, BYTE data2)
{
    static BYTE adlib_op[] = {0, 1, 2, 8, 9, 10, 16, 17, 18};
    static BYTE sbpro_op[] = { 0,  1,  2,   6,  7,  8,  12, 13, 14,
			      18, 19, 20,  24, 25, 26,  30, 31, 32};
    static WORD rg[] = {0x000,0x001,0x002,0x003,0x004,0x005,
			0x008,0x009,0x00A,0x00B,0x00C,0x00D,
			0x010,0x011,0x012,0x013,0x014,0x015,
			0x100,0x101,0x102,0x103,0x104,0x105,
			0x108,0x109,0x10A,0x10B,0x10C,0x10D,
			0x110,0x111,0x112,0x113,0x114,0x115};

    if (OPL3)
    {
	register WORD reg = sbpro_op[channel];
	FMwriteReg(rg[reg]+regbase, data1);
	FMwriteReg(rg[reg+3]+regbase, data2);
    } else {
	register WORD reg = regbase+adlib_op[channel];
	FMwriteReg(reg, data1);
	FMwriteReg(reg+3, data2);
    }
}

/*
 * Write to channel a single value. To be used for register bases of
 * 0xA0, 0xB0 and 0xC0.
 */
void FMwriteValue(BYTE regbase, BYTE channel, BYTE value)
{
    static WORD ch[] = {0x000,0x001,0x002,0x003,0x004,0x005,0x006,0x007,0x008,
			0x100,0x101,0x102,0x103,0x104,0x105,0x106,0x107,0x108};
    register WORD chan;

    if (OPL3)
	chan = ch[channel];
    else
	chan = channel;
    FMwriteReg(regbase + chan, value);
}
--------------------------------- cut here ---------------------------------

Appendix B - Detection Methods

OPL2 Detection

An official method of Adlib (OPL2) detection is:

1. Reset Timer 1 and Timer 2: write 60h to register 4.
2. Reset the IRQ: write 80h to register 4.
   Note: Steps 1 and 2 can't be combined together.
3. Read status register: read port base+0 (388h). Save the result.
4. Set Timer 1 to FFh: write FFh to register 2.
5. Unmask and start Timer 1: write 21h to register 4.
6. Wait in a delay loop for at least 80 usec.
7. Read status register: read port base+0 (388h). Save the result.
8. Reset Timer 1, Timer 2 and IRQ as in steps 1 and 2.
9. Test the results of the two reads: the first should be 0, the second should be C0h. If either is incorrect, then the OPL2 is not present.

Notes:

1. You should AND the result bytes with E0h because the unused bits are undefined.
2. This testing method doesn't work in some SoundBlaster compatible cards.

OPL3 Detection

1. Detect OPL2. If present, continue.
2. Read status register: read port base+0.
3. AND the result with 06h.
4. If the result is zero, you have OPL3, otherwise OPL2.

Another possible detection method for distinguishing between SB Pro I and SB Pro II would be to try to detect OPL2 at I/O port base+0 and then at port base+2. The first test should succeed and the second should fail if OPL3 is present. (Remember: SB Pro I contains twin OPL2 chips at addresses base+0 and base+2, while SB Pro II contains one OPL3 chip at I/O address base+0 thru base+3).

The BLASTER Environment Variable

Perhaps the most recommended "detection" method. Reading this variable avoids blindfold I/O port scanning and possible device conflicts. The user is responsible for its proper setting.

The variable has this format:

A: Base I/O address given in hex. For most Sound Blasters the default is 220.
I: IRQ Number (decimal). Default 7 (old SB and SB Pro), 5 (SB 16, etc.).
D: DMA Number (decimal). Default 1.
H: High DMA Number (decimal). Default 5 (on SB 16 and newer cards only)
P: MPU-401 MIDI port (hexadecimal). Default 330 (on SB 16 and newer cards)
E: EMU-8000 base port (hexadecimal). Default 620 (on AWE32 and newer cards)
T: Card Type (decimal):

Examples:

References

Title:		The PC Games Programmers Encyclopedia
Authors:	Mark Feldman and many others on Usenet and Internet
WWW:		http://www.qzx.com/pc-gpe/
FTP:		ftp://x2ftp.oulu.fi/pub/msdos/programming/gpe/pcgpe10.zip - 700KB

Title:		Sound Blaster - The Official Book
Authors:	Richard Heimlich, David M. Golden, Ivan Luk, Peter M. Ridge
Publishers:	Osborne/McGraw Hill
ISBN:		0-07-881907-5

Title:		The SoundBlaster Developer Kit
Publishers:	Creative Labs Inc
		Creative Technology PTE LTD

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