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                          Programming the AdLib/Sound Blaster
                                    FM Music Chips
                               Version 2.0 (24 Feb 1992)

                      Copyright (c) 1991, 1992 by Jeffrey S. Lee

                                   jlee@smylex.uucp

                            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.

     |   Changes from Version 1 of the file will be indicated by the use of change
     |   bars in the left-hand margin.

                             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 Blaster Pro is capable of stereo FM music, which is accessed
     |   in exactly the same manner.  Ports 0220 and 0221 (hex) are the address/
     |   data ports for the left speaker, and ports 0222 and 0223 (hex) are the
     |   ports for the right speaker.  Ports 0388 and 0389 (hex) will cause both
     |   speakers to output sound.

         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 AdLib manual gives the wait times in microseconds: three point three
     |   (3.3) microseconds for the address, and twenty-three (23) microseconds
     |   for the data.
     |
     |   The most accurate method of producing the delay is to read the register
     |   port six times after writing to the register port, and read the register
     |   port thirty-five times after writing to the data port.

         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 388.  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

     |                          Detecting a Sound Card
     |
     |   According to the AdLib manual, the 'official' method of checking for a
     |   sound card is as follows:
     |
     |      1)  Reset both timers by writing 60h to register 4.
     |      2)  Enable the interrupts by writing 80h to register 4.  NOTE: this
     |          must be a separate step from number 1.
     |      3)  Read the status register (port 388h).  Store the result.
     |      4)  Write FFh to register 2 (Timer 1).
     |      5)  Start timer 1 by writing 21h to register 4.
     |      6)  Delay for at least 80 microseconds.
     |      7)  Read the status register (port 388h).  Store the result.
     |      8)  Reset both timers and interrupts (see steps 1 and 2).
     |      9)  Test the stored results of steps 3 and 7 by ANDing them
     |          with E0h.  The result of step 3 should be 00h, and the
     |          result of step 7 should be C0h.  If both are correct, an
     |          AdLib-compatible board is installed in the computer.
     |
     |
     |                              Making a Sound
     |
     |   Many people have asked me, upon reading this document, what the proper
     |   register values should be to make a simple sound.  Well, here they are.
     |
     |   First, clear out all of the registers by setting all of them to zero.
     |   This is the quick-and-dirty method of resetting the sound card, but it
     |   works.  Note that if you wish to use different waveforms, you must then
     |   turn on bit 5 of register 1.  (This reset need be done only once, at the
     |   start of the program, and optionally when the program exits, just to
     |   make sure that your program doesn't leave any notes on when it exits.)
     |
     |   Now, set the following registers to the indicated value:
     |
     |     REGISTER     VALUE     DESCRIPTION
     |        20          01      Set the modulator's multiple to 1
     |        40          10      Set the modulator's level to about 40 dB
     |        60          F0      Modulator attack:  quick;   decay:   long
     |        80          77      Modulator sustain: medium;  release: medium
     |        A0          98      Set voice frequency's LSB (it'll be a D#)
     |        23          01      Set the carrier's multiple to 1
     |        43          00      Set the carrier to maximum volume (about 47 dB)
     |        63          F0      Carrier attack:  quick;   decay:   long
     |        83          77      Carrier sustain: medium;  release: medium
     |        B0          31      Turn the voice on; set the octave and freq MSB
     |
     |   To turn the voice off, set register B0h to 11h (or, in fact, any value
     |   which leaves bit 5 clear).  It's generally preferable, of course, to
     |   induce a delay before doing so.
     |
     |
     |                             Acknowledgements
     |
     |   Thanks are due to the following people:
     |
     |   Ezra M. Dreisbach (ed10+@andrew.cmu.edu), for providing the information
     |     about the recommended port write delay from the AdLib manual, and the
     |     'official' method of detecting an AdLib-compatible sound card.
     |
     |   Nathan Isaac Laredo (gt7080a@prism.gatech.edu), for providing the
     |     port numbers for stereo sound on the Sound Blaster Pro.

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