Datasheet ay-3-8910, AY-3-8912 Datasheet (Microchip Technology)

Untitled

30-OCT-1999

This is the General Instruments AY-3-8910 / 8912
Programmable Sound Generator (PSG) data Manual.

This was scanned and converted using adobe capture
and adobe acrobat to convert it into a .pdf.

Keep in mind that the OCR function is not perfect
and you should be careful of typos and other errors
introduced by the conversion process.

Page 1

AY-3-8910/8912

PROGRAMMABLE

SOUND GENERATOR

DATA MANUAL

Note: Registers are in Octal. Chart shown on page 11 shows

Channel A amplitude as “RIO”. In reality it is addressed as an “8”.
“RI1” is really “9”;

“R12” is really “A” etc.

It has been found that the PSG works well in SIOO Buss

Applications using the system clock which by definition is 2MHZ.

“The 2MHZ should be divided by 2 to yield 1 MHZ to allow for lower

noise frequencies. This eliminates the need for an external clock as

shown on page 33.
Note: Pages 3-4; 30, 31, 60-64 have been excluded. The booklet

does include all information available at this time.

Portions of this book have been reprinted with permission from the
original General Instrument Ay-3-8910/8912 DATA MANUAL.
Neither General Instruments nor this company assume
responsibility for the accuracy or use of any of the information
described herein.

1 INTRODUCTION

It is apparent that any microprocessor is capable of producing
acceptable sounds with only a transducer if the processor has no
other tasks to perform while the sound is sustained. In real world
microprocessor use, however, video games need refreshing, key-

boards need scanning, etc. For example, in order to produce a single
channel of ninth octave C (8372 Hz) the signal needs attention every
sixty microseconds. Software required to produce this simple effect
and still perform other activities would in the least be very complex if
not impossible. In the extreme, random noise requires periodic atten­tion even more frequently.

This need for software-produced sounds without the constant
attention of the processor is now satisfied with the availability of the
General Instrument AY-3-8910 and AY-3-8912 Programmable Sound
Generators.

1.1

Description

The AY-3-8910/8912 Programmable Sound Generator (PSG) is a

Large Scale Integrated Circuit which can produce a wide variety of
complex sounds under software control. The AY-3-8910/8912 is

manufactured in Gl’s N-Channel Ion Implant Process. Operation

requires a single 5V power supply, a TTL compatible clock, and a

microprocessor controller such as the GI 16-bit CP1600/1610 or one
of Gl’s PIC 1650 series of b-bit microcomputers.

The PSG is easily interfaced to any bus oriented system. Its flexibility
makes it useful in applications such as music synthesis, sound
effects generation, audible alarms, tonesignalling and FSK modems.
The analog sound outputs can each provide 4 bits of logarithmic
digital to analog conversion, greatly enhancing the dynamic range of
the sounds produced.

In order to perform sound effects while allowing the processor to
continue its other tasks, the PSG can continue to produce sound
after the initial commands have been given by the control processor.
The fact that realistic sound production often involves more than one
effect is satisfied by the three independently controllable channels
available in the PSG.

All of the circuit control signals are digital in nature and intended to
be provided directly by a microprocessor/microcomputer. This
means that one PSG can produce the full range of required sounds
with no change in external circuitry. Since the frequency responseof
the PSG ranges from sub-audible at its lowest frequency to post­audible at its highest frequency, there are few sounds which are
beyond reproduction with only the simplest electrical connections.

Since most applications of a microprocessor/PSG system would also
require interfacing between the outside world and the microproces­sor, this facility has been designed into the PSG. The AY-3-8910 has
two general purpose 8-bit I/O ports and is supplied in a 40 lead
package; the AY-3-8912 has one port and 28 leads.

1.2 > Full software control of sound generation.
> Interfaces to most 8-bit and 16-bit microprocessors.

Features q Three independently programmed analog outputs.

> Two 8-bit general purpose I/O ports (AY-3-8910).
> One 8-bit general purpose I/O port (AY-3-8912).
> Single +5 Volt Supply.

13 This Data Manual is intended to introduce the techniques needed to

Scope

cause the AY-3-8910/8912 Programmable Sound Generator to per-

form in its intended fashion. All of the programs, programming, and

hardware designs have been tested to ensure that the methods are
practical rather than purely theoretical.

Although the techniquesdescribed will produce powerful results, the

range of sounds to be synthesized is so vast and the PSG capabilities
so varied that this guide should be viewed merely as an introduction
to the applications possibilities of the PSG.

Fig. 1 TYPICAL SYSTEM DIAGRAM

2 ARCHITECTURE

The AY-3-8910/8912 is a register oriented Programmable Sound
Generator (PSG). Communication between the processor and the
PSG is based on the concept of memory-mapped I/O. Control
commands are issued to the PSG by writing to 16 memory-mapped

registers. Each of the 16 registers within the PSG is also readable so
that the microprocessor can determine, as necessary, present states
or stored data values.

All functions of the PSG are controlled through its 16 registers which
once programmed, generate and sustain thesounds, thus freeing the
system processor for other tasks.

2.1

An internal block diagram of the PSG showing the various functional

Basic

blocks and data flow is shown in Fig. 2.

Functional

Blocks

2.1.1 REGISTER ARRAY

The principal element of the PSG is the array of 16 read/write control
registers. These 16 registers look to the CPU as a block of memory
and as such occupy a 16 word block out of 1,024 possible addresses.
The 10 address bits (8 bits on the common data/address bus, and 2
separate address bits A8 and *A9) are decoded as follows:

i

The four low order address bits select one of the 16 registers

(RO--

R17*).

The six high order address bits function as “chip selects” to

control the tri-state bidirectional buffers (when the high order
address bits are “incorrect”, the bidirectional bulfers are forced to a

high impedance state). High order address bits A9 A8 are fixed in the

PSG design to recognize a 01 code; high order address bits

DA7--

DA4 may be mask-programmed to any 4-bit code by a special order
factory mask modification. Unless otherwise specified, address bits

DA7--DA4

are programmed to recognize only a 0000 code. A valid
high order address latches the register address (the low order 4 bits)
in the Register Address Latch/Decoder block. A latched address will
remain valid until the receipt of a new address, enabling multiple

reads and writes of the same register contents without the need for

redundant re-addressing.

21

Basic

Functional

Blocks

(cont.)

Conditioning of the Register Address Latch/Decoder and the Bidi­rectional Buffers to recognize the bus function required (inactive,
latch address, write data, or read data) is accomplished by the Bus
Control Decode block.

The function of each of the 16 PSG registers and the data flow of each
register’s contents are shown in context in Fig. 2 and explained in
detail in Section 3, “Operation”. For reference purposes, the Register
Array details are reproduced in Fig. 3.

2.1.2 SOUND GENERATING BLOCKS

The basic blocks in the PSG which produce the programmed sounds

include:

Tone Generators

Noise Generator

Mixers

Amplitude Control

Envelope Generator

D/A Converters

produce the basic square wave tone frequen­cies for each channel (A,B,C)

produces a frequency modulated pseudo
random pulse width square wave output.

combine the outputs of the Tone Generators
and the Noise Generator. One for each chan­nel (A,B,C).
provides the D/A Converters with either a
fixed or variable amplitude pattern. The fixed
amplitude is under‘ direct ‘CPU control; the
variable amplitude is accomplished by using
the output of the Envelope Generator.

produces an envelope pattern which can be
used to amplitude modulate the output of
each Mixer.
the three D/A Converters each produce up to
a 16 level output signal as determined by the
Amplitude Control.

2.1.3 I/O PORTS

Two additional blocks are shown in the PSG Block Diagram which

have nothing directly to do with the production of sound-these are
the two I/O Ports (A and B). Since virtually all uses of microproces­sor-based sound. would require interfacing between the outside
world and the processor, this facility has been included in the PSG.

Data to/from the CPU bus may be read/written to either of two 8-bit
I/O Ports without affecting any other function of the PSG. The I/O

Ports are TTL-compatible and are provided with internal pull-ups on
each pin. Both Ports are available on the AY-3-8910; only I/O Port A is
available on the AY-3-8912.

2.2

PIN Assignments

The AY-3-8910 is supplied in a 40 lead dual in-line package with the
pm assignments as shown in Fig. 4. The AY-3-8912 is supplied in a28

lead dual in-line package with the pin assignments as shown in Fig. 5.

Fig. 4 AY-3-8910 PIN ASSIGNMENTS

/kage

with the

R

pplied in a 28
own in Fig. 5.

IANNEL

C

2.3 DA7--DA0 (input/output/high impedance): pins30--37 (AY-3-8910)

Pin Functions Data/Address 7-0:

pins 21--28 (AY-3-8912)

These 8 lines comprise the 8-bit bidirectional bus used by the
microprocessor to send both data and addresses to the PSG and to
receive data from the PSG. In the data mode, DA7--DA0 correspond
to Register Array bits B7--B0. In the address mode, DA3-DA0 select
the register # (O--178) and DA7--DA4 in conjunction with address
inputs A9 and A8 form the high order address (chip select).

A8 (input): pin 25 (AY-3-8910)

pin 17 (AY-3-8912)

*A9 (input): pin 24 (AY-3-8910)

(not provided on AY-3-8912)

*Address 9, Address 8

These “extra” address bits are made available to enable the position­ing of the PSG (assigning a 16 word memory space) in a total 1,024
word memory area rather than in a 256 word memory area as defined
by address bits DA7--DA0 alone. If the memory size does not require
the use of these extra address lines they may be leftunconnected as
each is provided with either an on-chip pull down (A9) or pull-up (A8)
resistor. In “noisy” environments, however, it is recommended that
A9 and A8 be tied to an external ground and +5V, respectively, if they
are not to be used.

RESET

(input): pin 23 (AY-3-8910)

pin 16 (AY-3-8912)

For initialization/power-on purposes, applying logic “0” (ground)
to the Reset pin will reset all registers to “0”. The Reset pin is provided
with an on-chip pull-up resistor.

CLOCK (input): pin 22 (AY-3-8910)

pin 15 (AY-3-8912)

This TTL-compatible input supplies the timing reference for the
Tone, Noise and Envelope Generators.

BDIR, BC2, BCl (inputs): pins 27,28,29 (AY-3-8910)

pins 18,19,20 (AY-3-8912)

Bus DIRection, Bus Control 2,l

These bus control signals are generated directly by Gl’s CP1600
series of microprocessors to control all external and internal bus
operations in the PSG. When using a processor other than the
CP1600, these signals can be provided either by comparable bus
signalsor by simulating the signals on I/O lines of the processor. The
PSG decodes these signals as illustrated in the-following:

2.3

Pin Functions

(cont.)

While interfacing to a processor other than the CP1600 would simply

require simulating the above decoding, the redundancies in the PSG

functions vs. bus control signals can be used to advantage in that

only four of the eight possibledecoded bus functions are required by

the PSG. This could simplify the programming of the bus control

signals to the following, which would only require that the processor

generate two bus control signals (BDIR and BCl, with BC2 tied to

+5v):

Each of these signals is the output of its corresponding D/A
Converter, and provides an up to 1V peak-peak signal representing

the complex sound waveshape generated by the PSG.
IOA7--IOAO (input/output): pins 14--21 (AY-3-8910)

pins 7--14 (AY-3-8912)

IOB7--1OB0 (input/output): pins 6--13 (AY-3-8910)

(not provided on AY-3-8912)

Input/Output A7-- AO, B7-- B0

Each of these two parallel input/output ports provides 8 bits of

parallel data to/from the PSG/CPU bus from/to any external devices
connected to the IOA or IOB pins. Each pin is provided with an on­chip pull-up resistor, so that when in the “input” mode, all pins will
read normally high. Therefore, the recommended method for scan­ning external switches, for example, would be to ground the input bit.

.

TEST 1:

pin 39 (AY-3-8910)
pin 2 (AY-3-8912)

TEST

2: pin 26 (AY-3-8910)

(not connected on AY-3-8912)

These pins are for GI test purposes only and should be left open-&
not use as tie-points.

Vcc:

pin 40 (AY-3-8910)

pin 3 (AY-3-8912)

Nominal +5Volt power supply to the PSG.

Vss:

pin 1 (AY-3-8910)

pin 6 (AY-3-8912)

Ground reference for the PSG.

2.4 Since the PSG functions are controlled by commands from the

Bus Timing

system processor, the common data/address bus (DA7--DAO) re­quires definition as to its function at any particular time. This is
accomplished by the processor issuing bus control signals, previ­ously described, defining the state of the bus; the PSG then decodes
these signals to perform the requested task.

The conditioning of these bus control signals by the processor is the
same as if the processor were interacting with RAM: (1) the processor
outputs a memory address; and (2) the processor either outputs or
inputs data to/from the memory. The “memory” in this case is the

PSG’s array of 16 read/write control registers.

The timing relationships in issuing the bus control signals relative to
the data or address signals on the bus are reviewed in general in the
following section, and in detail in Section 7, Electrical Specifications.

2.5 While the state flow for many microprocessors can be somewhat

State Timing

involved for certain operations, the sequence of events necessary to
control the PSG is simple and straightforward. Each of the three
major state sequences (Latch Address, Write to PSG, and Read from
PSG) consists of several operations (indicated below by rectangular
blocks), defined by the pattern of bus control signals (BDIR, BC2,
BCl).

The functional operation and relative timing of the PSG control
sequences are described in the following paragraphs (in all exam­ples, BC2 has been assumed to be tied to logic “1”, +5V).

2.5.1 ADDRESS PSG REGISTER SEQUENCE
The “Latch Address.“. sequence is normally an integral part of the
write or read sequences, but for simplicity is illustrated here as an

individual sequence. Depending on the processor used the program
sequence will normally require four principal microstates: (1) send
NACT (inactive); (2) send INTAK (latch address); (3) put address on
bus: (4) send NACT (inactive). [Note: within the timing constraints
detailed in Section 7, steps (2) and (3) may be interchanged.]

2.5.2 WRITE DATA TO PSG SEQUENCE
The “Write to PSG” sequence, which would normally follow immedi-

ately after an address sequence, requires four principal microstates:
(1) send NACT (inactive); (2) put data on bus; (3) send DWS (write to
PSG); (4) send NACT (inactive).

2.5.3 READ DATA FROM PSG SEQUENCE
As with the “Write to PSG” sequence, the ”Read from PSG” sequence

would also normally follow immediately after an address sequence.
The four principal microstates of the read sequence are: (1) send
NACT (inactive); (2) send DTB (read from PSG); (3) read data on bus;

(4) send NACT (inactive).

2.5.4 WRITE TO/READ FROM l/O PORT SEQUENCE
Since the two I/O Ports (A and B) each have an 8-bit register assigned

as a data store, writing to or reading from either port is identical to
writing or reading to any other register. Hence, the state sequences
are exactly-the same as described in the preceding paragraphs.

3 OPERATION

Since all functions of the PSG are controlled by the host processor
via a series of register loads, a detailed description of the PSG
operation can best be accomplished by relating each PSG function to
the control of its corresponding register. The function of creating or
programming a specific sound or sound effect logically follows the
control sequence listed:

Section

3.1

3.2

3.3

3.4

3.5

Operation

Registers

Function

Tone Generator Control

R0--R5

Program tone periods.

Noise Generator Control

R6

Program noise period.

Mixer Control

R7

Enable tone and/or noise
on selected channels.

Amplitude Control

R10--R12 Select “fixed” or “envelope-

variable” amplitudes.

Envelope Generator

R13--R15

Program envelope period

Control

and select envelope pattern.

3.1 The frequency of each square wave generated by the three Tone

Tone Generator

Generators (one each for Channels A, B, and C) is obtained in the

PSG by first counting down the input clock by 16, then by further

Control

counting down the result by the programmed 12-bit Tone Period

value. Each 12-bit value is obtained in the PSG by combining the

(Registers R1, R2, R3, R4, R5)

contents of the relative Coarse and Fine Tune registers, as illustrated
in the

following.

12-bit Tone Period (TP) to Tone Generator

Note that the 12-bit value programmed in the combined Coarse and
Fine Tune registers is a period value-the higher the value in the
registers, the lower the resultant tone-frequency.

Note also that due to the design technique used in the Tone Period
count-down, the lowest period value is 000000000001 (divide by 1)
and the hiqhest period value is 1111111‘11111 (divide by 4,09510).

The equations describing the relationship between the desired
output tone frequency and the input clock frequency and Tone
Period value are:

3.2

Noise Generator

CONTROL

(Register

R6)

The frequency of the noise source is obtained in the PSG by first
counting down the input clock by 16, then by further counting down
the result by the programmed 5-bit Noise Period value. This B-bit
value consists of the lower 5 bits (B4-B0) of register R6, as
illustrated in the following:

Noise Period

Register R6

Note that the 6-bit value in R11 is a period value-the higher the value
in the register, the lower the resultant noise frequency. Note also that,
as with the Tone Period, the lowest period value is00001 (divide by 1);
the highest period value is 11111 (divide by 3110).

The noise frequency equation is:

Mix

3.3 Register 7, is a multi-function Enable register which controls the

Mixer

Control-

three Noise/Tone Mixers and the two general purpose I/O Ports.

I/O Enable

The Mixers, as previously described, combine the noise and tone
frequencies for each of the three channels. The determination of
combining neither/either/both noise and tone frequencies on each

(Register R7)

channel is made by the state of bits B5--B0 of R7.
The direction (input or output ) of the two general purpose I/O Ports

(IOA and IOB) is determined by the state of bits B7 and B6 of R7.
These functions are illustrated in the following:

Mixer Control-I/O Enable

Register R7

3.4 The amplitudes of the signals generated by each of the three D/A

Amplitude

Converters (one each for Channels A, B, and C) is determined by the
contents of the lower 5 bits (B4--BO) of registers R10, Rl11, and R12 as

control

illustrated in the following:

Amplitude Control

(Registers R10, R11, R12)

Register #

Channel

R10

A

Rll

B

R12

C

amplitude

4-bit “fixed”

“Mode”

amplitude Level.

The amplitude “mode” (bit M) selects either fixed level amplitude
(M=0) or variable level amplitude (M=1). It follows then that bits L3-­L0, defining the value of a “fixed” level amplitude, are only active
when M=0. When fixed level amplitude isselected, it is “fixed” only in
the sense that the amplitude level is under the direct control of the
system processor (via bits D3--D0). Varying the amplitude when in
this “fixed” amplitude mode requires in each instance the direct
intervention of the system processor via an address latch/write data
sequence to modify the D3--D0 data.

When M=1 (select “variable” level amplitudes), the amplitudeof each
channel is determined by the envelope pattern as defined by the
Envelope Generator’s 4-bit output E3 E2 E1 EO.

The amplitude “mode” (bit M) can also be thought of as an “envelope
enable” bit; i.e., when M=0 the envelope is not used, and when M=1
the envelope is enabled. (A full description of the Envelope Gener­ator function follows in Section 3.5).

Fig. 6

The full chart describing all combinations of the 5-bit Amplitude
Control is as follows:

Amplitude Control

Register #

Channel

R10

A

R11

B

R12

C

Fig. 6 graphically illustrates a selection of variable level (envelope­controlled) amplitude where the 16 levels directly reflect the output
of the Envelope Generator. A fixed level amplitude would correspond
to only one of the levels shown, with the level directly determined by
the decimal equivalent of bits L3 L2 L1 L0.

VARIABLE AMPLITUDE CONTROL (M=1)

3.5

To accomplish the generation of fairly complex envelope patterns,

Envelope

two independent methods of control are provided in the PSG: first, it
is possible to vary the frequency of the envelope using registers R13

Generator

and R14; and second, the relative shape and cycle pattern of the
envelope can be varied using register R15. The following paragraphs

Control

explain the details of the envelope control functions, describing first

the envelope period control and then the envelope shape/cycle

(Registers R13, R14, R15)

control.

3.5.1

ENVELOPE PERIOD CONTROL (Registers R13, R14)

The frequency of the envelope is obtained in the PSG by first
counting down the input clock by 256, then by further counting down
the result by the programmed 16-bit Envelope Period value. This

16-bit value is obtained in the PSG by combining the contents of the
Envelope Coarse and Fine Tune registers, as illustrated in the

following:

Note that the 16-bit value programmed in the combined Coarse and
Fine Tune registers is a period value-the higher the value in the
registers, the lower the resultant envelope frequency.

Note also, that as with the Tone Period, the lowest period Value is

0000000000000001 (divide by 1); the highest period value is

1111111111111111 (divide by 65,53610).
The envelope frequency equations are:

To calculate the values for the contents of the Envelope Period
Coarse and Fine Tune registers, given the input clock and the desired
envelope frequencies, we rearrange the above equations, yielding:

3.5.2 ENVELOPE SHAPE/CYCLE CONTROL

(Register

R15)

The Envelope Generator further counts down the envelope fre­quency by 16, producing a 16-state per cycle envelope pattern as
defined by its 4-bit counter output, E3 E2 El E0. The particular shape
and cycle pattern of any desired envelope is accomplished by
controlling the count pattern (count up/count down) of the 4-bit
counter and by defining a single-cycle or repeat-cycle pattern.

This envelope shape/cycle control is contained in the lower 4 bits

(B3--B0) of register R15. Each of these 4 bits controls a function in

the envelope generator, as illustrated in the following:

Envelope Shape/Cycle
Control Register (R15)

The definition of each function is as follows:
Hold

when set to logic “1”, limits the envelope to one cycle,
holding the last count of the envelope counter (E3--

E0=0000 or 1111, depending on whether the envelope
counter was in a count-down or count-up mode, respec­tively).

Alternate when set to logic “1”,

the envelope counter reverses

count direction (up-down) after each cycle.

NOTE: When both the Hold bit and the Alternate bit are ones, the

envelope counter is reset to its initial count before holding.

3.5

Envelope

Generator

Control

(cont.)

Fig. 7

Attack when set to logic “1": the envelope counter will count up

(attack) from E3 E2 E1 E0=0000 to E3 E2 E1 E0=1111;
when set to logic “0”, the envelope counter will count
down (decay) from 1111 to 0000.

Continue when set to logic “1”, the cycle pattern will be as defined

by the Hold bit; when set to logic “0”, the envelope
generator will reset to 0000 after one cycle and hold at
that count.

To further describe the above functions could be accomplished by

numerous charts of the binary count sequence of E3 E2 E1 E0 for
each combination of Hold, Alternate, Attackand Continue. However,
since these outputs are used (when selected by the Amplitude
Control registers) to amplitude modulate the output of the Mixers, a
better understanding of their effect can be accomplished via a
graphic representation of their value for each condition selected, as
illustrated in Figs. 7 and 8.

ENVELOPE SHAPE/CYCLE CONTROL

3.6

Registers R16 and R17 function as intermediate data storage regis-

I/O Port Data

ters between the PSG/CPU data bus (DA0--DA7) and the two I/O
ports (IOA7-IOA0 and

IOB7--1OB0).

Both ports are available in the

Store

AY-3-8910; only I/O Port A is available in the AY-3-8912. Using

registers R16 and R17 for the transfer of

I/O

data has no effect at all

(Registers R16, R17)

on sound generation.
To output data from the CPU bus to a peripheral device connected

to I/O Port A would require only the following steps:

1. Latch address R7 (select Enable register)

2. Write data to PSG (setting B6 of R7 to “1”)

3. Latch address R16 (select IOA register)

4. Write data to PSG (data to be output on

I/O

Port A)

To input data from I/O Port A to the CPU bus would require the
following:

1. Latch address R7 (select Enable register)

2. Write data to PSG (setting B6 to R7 to “0”)

3. Latch address R16 (select IOA register)

4. Read data from PSG (data from I/O Port A)

Note that once loaded with data in the output mode, the data will
remain on the I/O port(s) until changed either by loading different
data, by applying a reset (grounding the Reset pin), or by switching to

the input mode.
Note also that when in the input mode, the contents of registers R16

and/or R17 will follow thesignals applied to the I/O port(s). However,

transfer of this data to the CPU bus requires a “read” operation as

described above.

3.7 Since the primary use of the PSG is to produce sound for the highly

D/A Converter

imperfect amplitude detection mechanism of the human ear, the D/A
conversion is performed in logarithmic steps with a normalized

Operation

voltage range of from 0 to 1 Volt. The specific amplitude control of
each of the three D/A Converters isaccomplished by the three sets of
4-bit outputs of the Amplitude Control block, while the Mixeroutputs
provide the base signal frequency (Noise and/or Tone).

Fig. 9 illustrates the D/A Converter output which would result if noise
and tones were disabled and an envelope-controlled variable ampli­tude were selected.

4 INTERFACING

4.1

Introduction

Since the AY-3-8910/8912 PSG must be used with support compo­nents, interfacing to the circuit is an obvious requirement. The PSG is
designed to be controlled by a microprocessor or microcomputer,
and drive directly into analog audio circuitry. It provides the link
between the computer and a speaker to provide sounds or sound
effects derived from digital inputs.

The following paragraphs provide examples and illustrations show­ing the ease with which an AY-3-8910/8912 Programmable Sound
Generator may be utilized in a microprocessor/microcomputer
system.

Fig. 14 SYSTEM BLOCK DIAGRAM

,

4.2

An economical solution to providing a system clock is shown in Fig.

15. It consists of a 3.579545MHz standard color burst crystal, a

Clock

CD4089 CMOS inverter, and a CD4013 to divide the color burst

Generation

frequency in half. The clock produced for the PSG runs at a

1.7897725MHz rate. Depending on the microcomputer used, its clock
should be selected within its specified value.

Fig. 15 CLOCK GENERATION

4.3

Audio Output

Interface

Fig. 16

Fig. 16 illustrates the audio output connections to a commercially
available LM386 audio amplifier. It shows channels A, B, and C
summed together to enable complex waveforms to becomposed and
amplified through a single external amplifier. These channels may be
individually amplified through separate channels for more exotic
sound systems.

Each output channel is individually controlled by separateamplitude

registers (R10, R11, R12) and an enable register (R7) in the PSG.

AUDIO OUTPUT INTERFACE

4.4

The ROM or PROM shown connected to the PSG in Fig. 17 illustrates

External

an option for providing additional data information for processor
support. The two I/O registers within the PSG are used in this case to

Memory

address the memory via I/O Port A (8 Bits) and read data from the
memory via I/O Port B (8 Bits).

Access A

n

example of the bus control sequence to address and read an
external memory connected to I/O ports A and B would be as follows
(Assume Port A addresses and Port B reads):

Bus codes

Bus Control

BDIR BC2 BC1 Explanation of Bus Data (DA7--DA0)

Latch address

1 1

1

00000111: Latch R7 to program I/O Ports

Write to PSG

1 1

0 01000000: Set B7. B6 to 0, 1 respectively

Latch address

1 1

1

00001110: Latch R16 to address memory

Write to PSG

1 1

0 00000001: Address data to memory

Latch address

1 1100001111: Latch R17 to read memory

Read from PSG 0 11XXXXXXXX: Memory data contained in R17
NOTE: BC2 in the above Bus Codes may be permanently tied to +5V thus

requiring only two bus control lines for all control operations (refer to
Section 2.3 for a complete explanation).

Also, RAM or EAROM may be used in place of the ROM or PROM
shown by altering the program to use PORT B as an I/O. Port B then
will be able to write data as an output and read data as an input.

Fig. 17 EXTERNAL MEMORY ACCESS

I

4.5

In Fig. 18, the lines identified DA7--DA0 are the input/output bus bits

Microprocessor/

7--0. This 8 bit bus is used to pass all data and address information

between the AY-3-8910/8912 and the system processor.

Microcomputer

BC1, BC2 and BDIR are bus control signals generated by the

Interface

processor to direct all bus operations. These operations are identi­fied as Latch Address, Write to PSG, Read from PSG, and Inactive.

The following Sections detail specific interfaces to several popular

microprocessors/microcomputers.

Fig. 18 MICROPROCESSOR/MICROCOMPUTER INTERFACE

4.6 Fig. 19 shows the schematic of an AY-3-8910 demonstrator circuit.

Interfacing

This configuration uses a PIC 1650 as the main controller in the
circuit. The PIC 1650 is used to scan the keyboard, fetch data from
the PROMS, writedata to the AY-3-8910 and provide the timing for the

to the PIC 1650

AY-3-8910.

The interfacing is direct since the PIC 1650 and the AY-3-8910
operate with compatible supplies and input/output voltages.

This particular schematic illustrates how a microcomputer with
additional memory can produce a stand-alone music and sound
effects circuit. The circuit as shown operates with manual keyboard
selections.

As Fig. 19 shows, the design for the interface connects directly to the

output pins of the 1650 and the BC1, BC2, BDIR pins. The software

then has the responsibility of manipulating these signals to signal the

PSG to perform the proper address latch, read or write operations.
The program routine in this section illustrates code which is used in a

hand-held demonstrator unit. This demonstration unit illustrates the
range of PSG capabilities, including music, sound effects and I/O

control. Note that the generalized routines perform the address

latching before every read for convenience.

The “READ ROM” routine illustrates use of the generalized read and
write routines to access the outside world through the PSG to read
and write.

4.6

Interfacing

to the PIC 1650

(Cont.)

Fig. 19 PIC 1650/AY-3-6910 SYSTEM EXAMPLE

4.7

As shown in Fig. 20, the wiring is direct between the AY-3-8910 and a

Interfacing to the

CP1600/1610 microprocessor. The levels are compatible thus elimi­nating any need for level converters. Even the terminology between

CP1600/1610

the IC’s remains constant to provide simple-to-follow connections.
The CP1600/1610 acts as a controller in this configuration fetching

data from ROM’s contained elsewhere in the system. The CP1600/

1610 also acts as the bus controller developing the necessary timing

for the AY-3-8910.

4.7.1 WRITE DATA ROUTINE
The program necessary to write to a selected register is as follows:

MVI value, R0; move in value to be written

MVO R0, Reg; write to register

The routine to load all registers with the same value is as follows:

MVII Reg 0, R4
CLRR R0

Here MVO@ RO, R4

CMPI Reg 0 + 17, R4
BLT Here

4.7.2 READ DATA ROUTINE
The routine to read from a selected register is as follows:

MVI Reg, RO; get data from reg in R0
MVO R0, value; store in memory

Fig. 20 CP1600/1610/AY-3-8910 INTERFACE

4.8

An M6800 microprocessor can be interfaced with an AY-3-8910/8912

Interfacing

through the addition of an M6820 PIA chip. The I/O portsdesignated
as PA0 to PA7 are used as the 8 bit bus lines and I/O ports PB0 to PB2

to the M6800

are used as the bus control lines. The software routines shown are
used to control the latch address, write data, and read data functions
for the AY-3-8910/8912.

4.8.1 LATCH ADDRESS ROUTINE
;AT ENTRY, B HAS ADDRESS VALUE

LATCH CLRA

STAA 8005 ;GET D DIR A
LDAA #FF
STAA 8004 ;OUTPUTS

LDAA #4
STAA 8005 ;GET PERIPHERAL A
STAB 8004 ;FORM ADDR

STAA 8006

CLRA

STAA 8006 ;LATCH ADDRESS

RTS ;RETURN

4.8.2 WRITE DATA ROUTINE
;AT ENTRY, B HAD DATA VALUE

WRITE STAB 8004 ;FORM DATA

LDAA #6 ;DWS

STAA 8006

CLRA

STAA 8006 ;WRITE DATA

RTS ;RETURN
I

4.8.3 READ DATA ROUTINE
;AFTER READ, B HAS READ DATA

READ STA A 8005 ;GET D DIR

STA A 8004 ;INPUTS
LDAA #4
STA A 8005 ;GET PERIPHERAL
DECA
STA A 8006 ;READ MODE
LDA B 8004 ;READ DATA
CLRA
STA A 8006 ;REMOVE READ MODE
RTS ;RETURN

Fig. 21 M6800/AY-3-8910 INTERFACE

4.9

Interfacing

to the 8080

The sample S100 bus design provides for reading and writing the

PSG using only an 8080 “IN” or “OUT” instruction to the proper

address. Another feature of the design is the provision for multiple

PSG devices to be connected to a single bus. The system described is

presently running two PSG’s,

one

to each of

two

stereo channels.

S100 Bus

As can be seen from the read and write routines in the illustrative
program, the program overhead necessary to communicate with the

PSG is minimal.

4.9.1 LATCH ADDRESS ROUTINE

PORTADDR EQU 80H ;ADDRESS TRANSFER PORT ADDRESS
PORTDATA EQU 81H ;DATA TRANSFER PORT ADDRESS

THIS ROUTINE WILL TRANSFER THE CONTENTS OF
;8080 REGISTER C TO THE PSG ADDRESS REGISTER
PSGBAR

MOV A,C ;GET C IN A FOR OUT

OUT

PORTBAR ;SEND TO ADDRESS PORT

RET

4.9.2 WRITE DATA ROUTINE

ROUTINETO WRITE THE CONTENTS OF 8080 REGISTER B
;TO THE PSG REGISTER SPECIFIED BY 8080 REGISTER C

PSGWRITE CALL PSGBAR ;GET ADDRESS LATCHED

MOV A.B, ;GET VALUE IN A FOR TRANSFER
RET PORTDATA ;PUT TO PSG REGISTER

4.9.3 READ DATA ROUTINE

ROUTlNE TO READ THE PSG REGISTER SPECIFIED
;BY THE 8080 REGISTER C AND RETURN THE DATA
;IN 8080 REGISTER B

PSGREAD CALL PSGBAR

IN

PORTDATA ;GET REGISTER DATA
MOV B,A GET IN TRANSFER REGISTER
RET

5 MUSIC GENERATION

The production of music involves the creation of series of frequen­cies which are pleasing to the human ear (setting critical evaluation
aside). This involves essentially mathematical relationships, making
the application ideal for digital devices. For example, the shifting up
or down in octaves is a multiplication or division by a power of 2,
which is a simple shift operation for most microprocessors.

Another factor in music generation is “communication”. The com­poser must be able to convey his tune ideas so that a musician or
group of musicians can reproduce the composer’s ideas-often on
widely differing instruments. This concept involves “tuning” the
instruments to a standard set of frequencies and following a set
rhythm pattern. The tuning frequency most widely used is based on
the third octave note “A” of 440Hz, the “Equal Tempered Chromatic
Scale”.

Although it is easy to construct recognizable tunes using only one

note at a time, the simultaneous sounding of more than one note to
produce chords and counterpoint vastly increases the quality of the
sound. This feature is easily achieved in the PSG since three
channels are provided, each independently programmable.

Note

5.1 Since notes are formed by sustaining a particular frequency for a

Generation

preset period of time at a varying amplitude, the PSG performs this

function with a series of simple register loads. The method used in

many cases is to obtain register load values for first octave notes and

to shift to the correct octave at playtime.

The chart in Fig. 23 lists a full 8 octaves of notes from a low of Cl
(32.703Hz) to a high of B8 (7902.080Hz). Assuming an input clock

frequency of 1.78977MHz (one half the standard “color” crystal
frequency of 3579545MHz), and applying the formulas of Section 3.1
for calculating Tone Period register load values, results in the

register values shown. The nature of the PSG divider scheme

produces a high degree of accuracy for low frequencies, less for high
frequencies. This can be seen in the chart in the comparison of “ideal
frequencies” and “actual frequencies”, with the ideal frequencies

being those of the Equal Tempered Chromatic Scale, and the actual

frequencies being the “best fit” values from the formula calculation.

5.2

Tune Entry/

Playback

53

Tune Variations

One of the methods of entering a composition into a computer
memory would be to utilize a keyboard to pass number and
alphabetic information concerning the composer’s wishes. An alter­nate method would be to scan a positional series of switches (like a

piano keyboard) to determine note, volume and duration data.

Since flexibility in tune entry is desired, it is important to allow the
composer to specify certain constants of entry such as octave, pitch
or tempo, and have these entries normalized to a known value.

One of the significant features of a microcomputer based music
player is the ability to modify the tune once it has been recorded.
Among the simpler variations are:

5.3.1 OCTAVE SHIFT

If an octave constant is added to the octave of the recorded note prior

to storing the value in the PSG register, dynamic pitch changes can

be obtained. The programming effect would be to shift one bit left for
each lower octave and one bit right for each higher octave. For
example, the effect will be that a tune written to play on a piano will
sound like bells if a multiple octave up modification is performed.

5.3.2 KEY

One measure of the virtuosity of a musician is his ability to modify the
“key” or suboctave shift of a composition. The logical description of
key transposition is to shift each note up or down by a predetermined

number of notes from the original. For example, a piece written in C

and played in C# would have all C notesshifted to C#, C# shifted to D,
etc. (Note that the case must be considered where B of one octave is
shifted to C of the next higher octave.) All of theseoperations require
that the one of twelve note identification must be retained in the
recorded representation.

5.3.3 TEMPO

The duration of each recorded note is best expressed in terms of
“ticks” of an overall “tempo clock”. At playtime, the total duration can
be obtained by programatically multiplying the individual note to
“slow down” or “speed up” the tune without changing the crucial time
relationship between the notes. This can be accomplished by
imbedding the note timing loops within the tempo timing loops for
simple operation.

5.3.4 CHORDS
There are-certain combinations of notes which when played simul-

taneously produce pleasant combinations. These “chords” can be
easily formed from a base note by performing octave and key
changes on two notes, which are played with the main note. These

relationships are illustrated in Fig. 24, which lists the various note
constants which will produce musical chords. A chord with a
particular quality may be formed by playing its root, a 3rd Minor or
Major, and other notes from the chord chart. For example, a C Major

chord is formed from C(/2), E(/2), and G(/2).

Fig. 24 CHORD SELECTION CHART

5.4

5.4.1 RELATIVE CHANNEL VOLUME

VARIATION

The independently programmable amplitude control for each chan­nel allows up to 16 levels if using the processor controlled amplitude
mode (bit 4 of registers 10, 11 or 12=0). In the case of a
decaying or steady note, when a note is played or “fired”, a frequency
may be set up in the coarse and fine tune registers and then an
amplitude value placed in the respective register 10, 11 or 12. The
value which is placed to play the tune can be an independent
variable, allowing channels to play their respective melody lines with
varying force.

5.4.2 DECAY

The main difference between a “piano” sound and an “organ” sound

is the speed with which the note loses volume. If all of the notes can be
decayed at a uniform rate, the automatic envelope generator can be
set to produce a decaying waveform. Each of the three channels can
have the same decay constant but differing playing times tosimulate

the same instrument with differing note-strike times.

Sound

5.4.3 OTHER EFFECTS

The addition of variable noise to any or all of the channels can
produce modification effects such “breathing” with a wind instru­ment. Or noise can be used alone to produce a drum rhythm. The fact
that the noise dominant frequencies are variable allows “synthesizer”

type effects with simple processor interaction.

Other pleasing effects include vibrato and tremolo, the cyclical

variation of the frequency and volume. Because an intelligent

microprocessor is controlling the effect, they can be all keyed to the

tune itself or to other external stimuli.

A

5.5

Applications

Fig. 25 ORGAN ENVELOPE GENERATION

While many applications of the PSG in music generation are
apparent, for instance in the area of toys and games, other applica­tions are possible even in the area of high accuracy sophisticated
musical instruments such as high-end electronic organs. With tone
frequencies generated from another source to meet the exacting
requirements of organ operation, the PSG can be used as a complex
envelope generator. The PSG is also effective for generating bass
notes and rhythms with percussion instruments, taking advantageof
the PSG’s high accuracy in producing low frequency notes. The
following paragraphs detail examples of these applications.

5.5.1 ORGAN ENVELOPE GENERATION

The envelope generation diagram shown in Fig. 25 illustrates how an
AY-3-8910 can be configured to produce envelopes for organ
voicing. All functions are controlled by a microcomputer.

The basis of this system consists of a master frequency generator
with a string of dividers. This produces all frequencies for the
keyboard. The microcomputer and the AY-3-8910 are actually used
to replace the usual components of voicing filters that would
ordinarily be used in an electronic organ.

The microcomputer shown is a Gl PIC 1650 controlled by inputsfrom

the keyboard keyer circuit and a control switch matrix. The keyer
inputs octave and key closure information to develop the envelope
amplitude and duration for the note to be played. The control switch
matrix can be used to control sustain and add other special effects.
The ROM shown connected to the AY-3-8910 is optional depending
on the amount of data necessary for the microcomputer.

The system shown here may also consist of multiple AY-3-8910’s all
controlled by a single microcomputer. It represents an economical
solution to developing voicing control with a minimum of compo­nents.

5.5

5.5.2 ORGAN RHYTHM GENERATION

Applications

The rhythm generation diagram (Fig. 26) illustrates a simplified
version of how a microcomputer can be implemented with the AY-3­8910 to provide a percussion instrument section for an electronic

(cont.) organ.

The microcomputer used in this case could be a GI PIC 1650 which
can be internally programmed to drive a series of AY-3-8910’s all
hardwired to an I/O port of the PIC. Each AY-3-8910 provides a
separate output envelope and frequency of the instrument it is to
synthesize.

The Rhythm Switch Matrix is used to select any preprogrammed
rhythm pattern and tempo from the PIC. The Instrument Select
switches allow manual in/out selection of the 8910’s via the A8 and A9
address lines providing additional instrument sound variations.
These switches are intended to be user-selected and mounted in a

convenient position on the instrument.

In addition, optional ROMs could be added to the PSG I/O ports,
saving microcomputer ports, to provide extra rhythm length or
number of patterns. These ROMs could also be replaced by EAROMs
to provide user rhythm programming from a modified Rhythm Switch
Matrix. The programmable rhythm feature could be used to add new
or original user rhythms to update the instrument.

Fig. 26 ORGAN RHYTHM GENERATION

6 SOUND EFFECTS GENERATION

One of the main uses of the PSG is to produce non-musical sound
effects to accompany visual action or as a feature in itself. The
following sections outline techniques and provide actual examples of
some popular effects. All examples are based on a 1.78977MHz PSG

clock.

6.1

Many effects are possible using only the tone generation capability of

Tone Only

the PSG without adding noise and without using the PSG’s envelope
generation capability. Examples of this type of effect would include

Effects

telephone tone frequencies (two distinct frequencies produced
simultaneously) or the European Siren effect listed in Fig. 27 (two
distinct frequencies sequentially produced).

Fig. 27 EUROPEAN SIREN SOUND EFFECT CHART

6.2

Some of the more commonly required sounds require only the use of

Noise Only

noise and the envelope generator (or processor control of channel
envelope if other channels are using the envelope generator).

Effects

Examples of this, which can be seen in Figs. 28 and 29, are gunshot
and explosion. In both cases pure noise is used with a decaying
envelope. In the examples shown the only changes are in the length
of the envelope as modified by the coarse tune register and in the
noise period. Note that a significantly lower explosion can be
obtained by using all three channels operating with the same
parameters.

Fig. 28 GUNSHOT SOUND EFFECT CHART

Octal

Register # Load Value

Explanatlon

Any not specified

000

R6

017

Set Noise period to mid-value.

R7

007

Enable Noise only on Channels A,B,C.

RlO

020

Rll

020

Select full amplitude range under direct

R12

020

control of Envelope Generator.

R14

020

Set Envelope period to 0.586 seconds.

R15

000

Select Envelope “decay”, one cycle only.

Fig. 29 EXPLOSION SOUND EFFECT CHART

Register #

Any not specified

R6

R7
R10
R11
R12
R14
R15

Octal

Load Value

Explanation

000
000

Set Noise period to max. value.

007

Enable Noise only, on Channels A,B,C.
020
020

Select full amplitude range under
020

direct control of Envelope Generator.
070

Set Envelope period to 2.05 seconds.

000

Select Envelope “decay”, one cycle only.

7 ELECTRICAL SPECIFICATIONS

6.4

Multi-Channel

Effects

Because of the independent architecture of the PSG, many rather
complex effects are possible without burdening the processor. For
example, the Wolf Whistle effect in Fig. 32 shows two channels in use
to add constant breath hissing noise to the three concentrated
frequency sweeps of the whistle. Once the noise is put on the
channel, the processor only need be concerned with the frequency
sweep operation.

Fig. 32

WOLF WHISTLE SOUND EFFECT CHART

Fig. 33

7 ELECTRICAL SPECIFICATIONS