
                      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



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                                   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.
