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Programming the AdLib/Sound Blaster (FM Music Chips), a Quick Reference Guide.
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Programming the AdLib/Sound Blaster (FM Music Chips), a Quick Reference Guide.
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Programming the AdLib/Sound Blaster
FM Music Chips
Quick Reference Guide

Copyright (c) 1991 by Jeffrey S. Lee

[email protected]



Warranty and Copyright Policy

This document is provided on an "as-is" basis, and its author makes
no warranty or representation, express or implied, with respect to
its quality performance or fitness for a particular purpose. In no
event will the author of this document be liable for direct, indirect,
special, incidental, or consequential damages arising out of the use
or inability to use the information contained within. Use of this
document is at your own risk.

This file may be used and copied freely so long as the applicable
copyright notices are retained, and no modifications are made to the
text of the document. No money shall be charged for its distribution
beyond reasonable shipping, handling and duplication costs, nor shall
proprietary changes be made to this document so that it cannot be
distributed freely. This document may not be included in published
material or commercial packages without the written consent of its
author.



Overview

Two of the most popular sound cards for the IBM-PC, the AdLib and the
Sound Blaster, suffer from a real dearth of clear documentation for
programmers. AdLib Inc. and Creative Labs, Inc. both sell developers'
kits for their sound cards, but these are expensive, and (in the case
of the Sound Blaster developers' kit) can be extremely cryptic.

This document is intended to provide programmers with a FREE source
of information about the programming of these sound cards.

The information contained in this document is a combination of
information found in the Sound Blaster Software Developer's Kit, and
that learned by painful experience. Some of the information may not
be valid for AdLib cards; if this is so, I apologize in advance.

Please note that numbers will be given in hexadecimal, unless otherwise
indicated. If a number is written out longhand (sixteen instead of 16)
it is in decimal. Bits within a byte are numbered from 0 (the rightmost,
least significant bit) to 7 (the leftmost, most significant bit). Sound
channels are likewise numbered; the nine channels will be designated as
channels 0 through 8.




Chapter One - Sound Card I/O

The sound card is programmed by sending data to its internal registers
via its two I/O ports:

0388 (hex) - Address/Status port (R/W)
0389 (hex) - Data port (W/O)

The sound card possesses an array of two hundred forty-four registers;
to write to a particular register, send the register number (01-F5) to
the address port, and the desired value to the data port.

After writing to the register port, you must wait twelve cycles before
sending the data; after writing the data, eighty-four cycles must elapse
before any other sound card operation may be performed.

The sound card registers are write-only.

The address port also functions as a sound card status byte. To
retrieve the sound card's status, simply read port 0388. The status
byte has the following structure:

7 6 5 4 3 2 1 0
+------+------+------+------+------+------+------+------+
| both | tmr | tmr | unused |
| tmrs | 1 | 2 | |
+------+------+------+------+------+------+------+------+

Bit 7 - set if either timer has expired.
6 - set if timer 1 has expired.
5 - set if timer 2 has expired.



Chapter Two - The Registers

The following table shows the function of each register in the sound
card. Registers will be explained in detail after the table. Registers
not listed are unused.

Address Function
------- ----------------------------------------------------
01 Test LSI / Enable waveform control
02 Timer 1 data
03 Timer 2 data
04 Timer control flags
08 Speech synthesis mode / Keyboard split note select
20..35 Amp Mod / Vibrato / EG type / Key Scaling / Multiple
40..55 Key scaling level / Operator output level
60..75 Attack Rate / Decay Rate
80..95 Sustain Level / Release Rate
A0..A8 Frequency (low 8 bits)
B0..B8 Key On / Octave / Frequency (high 2 bits)
BD AM depth / Vibrato depth / Rhythm control
C0..C8 Feedback strength / Connection type
E0..F5 Wave Select

The groupings of twenty-two registers (20-35, 40-55, etc.) have an odd
order due to the use of two operators for each FM voice. The following
table shows the offsets within each group of registers for each operator.


Channel 1 2 3 4 5 6 7 8 9
Operator 1 00 01 02 08 09 0A 10 11 12
Operator 2 03 04 05 0B 0C 0D 13 14 15

Thus, the addresses of the attack/decay bytes for channel 3 are 62 for
the first operator, and 65 for the second. (The address of the second
operator is always the address of the first operator plus three).

To further illustrate the relationship, the addresses needed to control
channel 5 are:

29 - Operator 1 AM/VIB/EG/KSR/Multiplier
2C - Operator 2 AM/VIB/EG/KSR/Multiplier
49 - Operator 1 KSL/Output Level
4C - Operator 2 KSL/Output Level
69 - Operator 1 Attack/Decay
6C - Operator 2 Attack/Decay
89 - Operator 1 Sustain/Release
8C - Operator 2 Sustain/Release
A4 - Frequency (low 8 bits)
B4 - Key On/Octave/Frequency (high 2 bits)
C4 - Feedback/Connection Type
E9 - Operator 1 Waveform
EC - Operator 2 Waveform



Explanations of Registers

Byte 01 - This byte is normally used to test the LSI device. All bits
should normally be zero. Bit 5, if enabled, allows the FM
chips to control the waveform of each operator.

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| unused | WS | unused |
+-----+-----+-----+-----+-----+-----+-----+-----+


Byte 02 - Timer 1 Data. If Timer 1 is enabled, the value in this
register will be incremented until it overflows. Upon
overflow, the sound card will signal a TIMER interrupt
(INT 08) and set bits 7 and 6 in its status byte. The
value for this timer is incremented every eighty (80)
microseconds.


Byte 03 - Timer 2 Data. If Timer 2 is enabled, the value in this
register will be incremented until it overflows. Upon
overflow, the sound card will signal a TIMER interrupt
(INT 08) and set bits 7 and 5 in its status byte. The
value for this timer is incremented every three hundred
twenty (320) microseconds.


Byte 04 - Timer Control Byte

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| IRQ | T1 | T2 | unused | T2 | T1 |
| RST | MSK | MSK | | CTL | CTL |
+-----+-----+-----+-----+-----+-----+-----+-----+

bit 7 - Resets the flags for timers 1 & 2. If set,
all other bits are ignored.
bit 6 - Masks Timer 1. If set, bit 0 is ignored.
bit 5 - Masks Timer 2. If set, bit 1 is ignored.
bit 1 - When clear, Timer 2 does not operate.
When set, the value from byte 03 is loaded into
Timer 2, and incrementation begins.
bit 0 - When clear, Timer 1 does not operate.
When set, the value from byte 02 is loaded into
Timer 1, and incrementation begins.


Byte 08 - CSM Mode / Keyboard Split.

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| CSM | Key | unused |
| sel | Spl | |
+-----+-----+-----+-----+-----+-----+-----+-----+

bit 7 - When set, selects composite sine-wave speech synthesis
mode (all KEY-ON bits must be clear). When clear,
selects FM music mode.

bit 6 - Selects the keyboard split point (in conjunction with
the F-Number data). The documentation in the Sound
Blaster manual is utterly incomprehensible on this;
I can't reproduce it without violating their copyright.


Bytes 20-35 - Amplitude Modulation / Vibrato / Envelope Generator Type /
Keyboard Scaling Rate / Modulator Frequency Multiple

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| Amp | Vib | EG | KSR | Modulator Frequency |
| Mod | | Typ | | Multiple |
+-----+-----+-----+-----+-----+-----+-----+-----+

bit 7 - Apply amplitude modulation when set; AM depth is
controlled by the AM-Depth flag in address BD.
bit 6 - Apply vibrato when set; vibrato depth is controlled
by the Vib-Depth flag in address BD.
bit 5 - When set, the sustain level of the voice is maintained
until released; when clear, the sound begins to decay
immediately after hitting the SUSTAIN phase.
bit 4 - Keyboard scaling rate. This is another incomprehensible
bit in the Sound Blaster manual. From experience, if
this bit is set, the sound's envelope is foreshortened as
it rises in pitch.
bits 3-0 - These bits indicate which harmonic the operator will
produce sound (or modulation) in relation to the voice's
specified frequency:

0 - one octave below
1 - at the voice's specified frequency
2 - one octave above
3 - an octave and a fifth above
4 - two octaves above
5 - two octaves and a major third above
6 - two octaves and a fifth above
7 - two octaves and a minor seventh above
8 - three octaves above
9 - three octaves and a major second above
A - three octaves and a major third above
B - " " " " " " "
C - three octaves and a fifth above
D - " " " " " "
E - three octaves and a major seventh above
F - " " " " " " "


Bytes 40-55 - Level Key Scaling / Total Level

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| Scaling | Total Level |
| Level | 24 12 6 3 1.5 .75 | <-- dB
+-----+-----+-----+-----+-----+-----+-----+-----+

bits 7-6 - causes output levels to decrease as the frequency
rises:

00 - no change
10 - 1.5 dB/8ve
01 - 3 dB/8ve
11 - 6 dB/8ve

bits 5-0 - controls the total output level of the operator.
all bits CLEAR is loudest; all bits SET is the
softest. Don't ask me why.


Bytes 60-75 - Attack Rate / Decay Rate

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

bits 7-4 - Attack rate. 0 is the slowest, F is the fastest.
bits 3-0 - Decay rate. 0 is the slowest, F is the fastest.


Bytes 80-95 - Sustain Level / Release Rate

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| Sustain Level | Release |
| 24 12 6 3 | Rate |
+-----+-----+-----+-----+-----+-----+-----+-----+

bits 7-4 - Sustain Level. 0 is the loudest, F is the softest.
bits 3-0 - Release Rate. 0 is the slowest, F is the fastest.


Bytes A0-B8 - Octave / F-Number / Key-On

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| F-Number (least significant byte) | (A0-A8)
| |
+-----+-----+-----+-----+-----+-----+-----+-----+

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| Unused | Key | Octave | F-Number | (B0-B8)
| | On | | most sig. |
+-----+-----+-----+-----+-----+-----+-----+-----+

bit 5 - Channel is voiced when set, silent when clear.
bits 4-2 - Octave (0-7). 0 is lowest, 7 is highest.
bits 1-0 - Most significant bits of F-number.

In octave 4, the F-number values for the chromatic scale and their
corresponding frequencies would be:

F Number Frequency Note
16B 277.2 C#
181 293.7 D
198 311.1 D#
1B0 329.6 E
1CA 349.2 F
1E5 370.0 F#
202 392.0 G
220 415.3 G#
241 440.0 A
263 466.2 A#
287 493.9 B
2AE 523.3 C


Bytes C0-C8 - Feedback / Algorithm

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| unused | Feedback | Alg |
| | | |
+-----+-----+-----+-----+-----+-----+-----+-----+

bits 3-1 - Feedback strength. If all three bits are set to
zero, no feedback is present. With values 1-7,
operator 1 will send a portion of its output back
into itself. 1 is the least amount of feedback,
7 is the most.
bit 0 - If set to 0, operator 1 modulates operator 2. In this
case, operator 2 is the only one producing sound.
If set to 1, both operators produce sound directly.
Complex sounds are more easily created if the algorithm
is set to 0.


Byte BD - Amplitude Modulation Depth / Vibrato Depth / Rhythm

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| AM | Vib | Rhy | BD | SD | TOM | Top | HH |
| Dep | Dep | Ena | | | | Cym | |
+-----+-----+-----+-----+-----+-----+-----+-----+

bit 7 - Set: AM depth is 4.8dB
Clear: AM depth is 1 dB
bit 6 - Set: Vibrato depth is 14 cent
Clear: Vibrato depth is 7 cent
bit 5 - Set: Rhythm enabled (6 melodic voices)
Clear: Rhythm disabled (9 melodic voices)
bit 4 - Bass drum on/off
bit 3 - Snare drum on/off
bit 2 - Tom tom on/off
bit 1 - Cymbal on/off
bit 0 - Hi Hat on/off

Note: KEY-ON registers for channels 06, 07, and 08 must be OFF
in order to use the rhythm section. Other parameters
such as attack/decay/sustain/release must also be set
appropriately.


Bytes E0-F5 - Waveform Select

7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| unused | Waveform |
| | Select |
+-----+-----+-----+-----+-----+-----+-----+-----+

bits 1-0 - When bit 5 of address 01 is set, the output waveform
will be distorted according to the waveform indicated
by these two bits. I'll try to diagram them here,
but this medium is fairly restrictive.

___ ___ ___ ___ _ _
/ \ / \ / \ / \ / | / |
/_____\_______ /_____\_____ /_____\/_____\ /__|___/__|___
\ /
\___/

00 01 10 11





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