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ZX Doze #01
27 апреля 1997 |
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THE AY-3-8910/8912 SOUND SYNTHESIZER IC
========================================
OVERVIEW
--------
The AY-3-8910/8912 is a sound generator IC containing
three tone generators and a white noise generator. In addition
to its sound producing capabilities, the AY-3-8910 has two 8-bit
I/O ports and the AY-3-8912 has one.
PINOUTS (FOR THE AY-3-8912 ONLY)
--------------------------------
+----+--+----+
Channel C out -+ 1 |__| 28 +- DAO
| |
Test 1 -+ +- DA1
| |
+5V -+ +- DA2
| |
Channel B out -+ +- DAЗ
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Channel A out -+ +- DAЧ
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GND -+ +- DAS
| |
IOA7 -+ +- DAб
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IOAб -+ +- DA7
| |
IOAS -+ +- BC1
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IOAЧ -+ +- BC2
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IOAЗ -+ +- BDIR
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IOA2 -+ +- A8
| | _____
IOA1 -+ +- RESET
| |
IOAO -+ 14 15 +- CLK
+------------+
DAO-DA7 are multiplexed data and address lines, as used
in the range of GI processors that this IC was originally part
of. The BC1 and BDIR pins are used to control the IC as follows:
Function BDIR BC1
Inactive 0 0
Read 0 1
Write 1 0
Latch address 1 1
In addition to using BC1 and BDIR, A8 should be taken
high to enable the chip. IOAO-IOA7 are the input/output pins
(the AY-3-8910 has an additional set marked IOBO-IOB7). The IC
does not contain an internal oscillator - the clock input to the
CLK pin should fall between 1MHz-2MHz, so a typical Z80 system's
clock would need to be divided.
REGISTERS
---------
The AY-3-8910/8912 contains 16 internal registers as
follows:
REGISTER FUNCTION RANGE
0 Channel A fine pitch 8-bit (0-255)
1 Channel A course pitch 4-bit (0-15)
2 Channel B fine pitch 8-bit (0-255)
3 Channel B course pitch 4-bit (0-15)
4 Channel C fine pitch 8-bit (0-255)
5 Channel C course pitch 4-bit (0-15)
6 Noise pitch 5-bit (0-31)
7 Mixer 8-bit (see below)
8 Channel A volume 4-bit (0-15, see below)
9 Channel B volume 4-bit (0-15, see below)
10 Channel C volume 4-bit (0-15, see below)
11 Envelope fine duration 8-bit (0-255)
12 Envelope course duration 8-bit (0-255)
13 Envelope shape 4-bit (0-15)
14 I/O port A 8-bit (0-255)
15 I/O port B 8-bit (0-255)
Notes:
- The AY-3-8912 does not contain register 15.
- The volume registers (8, 9 and 10) contain a 4-bit
setting but if bit 5 is set then that channel uses the envelope
defined by register 13 and ignores its volume setting.
- The mixer (register 7) is made up of the following
bits (low=enabled):
Bit: 7 6 5 4 3 2 1 0
_ _
I/O I/O Noise Noise Noise Tone Tone Tone
B A C B A C B A
The AY-3-8912 ignores bit 7 of this register.
ENVELOPES
---------
The AY-3-8910/8912 contains the following preset
envelopes or waveforms (set using control register 13). Note
that these affect volume only and not the pitch:
0 __________ single decay then off
4 /|_________ single attack then off
8 ||||| repeated decay
9 __________ single decay then off
10 ///// repeated decay-attack
_________
11 | single decay then hold
12 /|/|/|/|/|/ repeated attack
__________
13 / single attack then hold
14 ////// repeated attack-decay
15 /|_________ single attack then off
PITCH VALUES
------------
The course and fine pitch registers for each channel are
used in the following fashion (assuming channel A).
Registers 0 and 1 operate together to form channel A's
final pitch. The eight least significant bits are sent to
register 0 and the four most significant bits are sent to
register 1. The output frequency is equal to the IC's incoming
clock frequency divided by 16 and then further divided by the
number written to the course and fine pitch registers, so the
higher the number written to these, the lower the pitch. For
example, if a frequency of 1KHz was required and the IC's clock
frequency was 1MHz, a total division rate of 1000 would be
needed. The sound generator itself divides by 16 so the course
and fine pitch registers must provide a further division by 62.5
(due to the fact that 1000/16 is 62.5). A division rate of 62 or
63 will be accurate enough, since the registers can only store
whole numbers. Therefore, 62 or 63 would be written to register
0 and 0 would be written to register 1.
The following frequency table may be useful in musical
applications:
Note Frequency (Hz) Note Frequency (Hz)
A 220 D# 311.1
A# 233.3 E 329.63
B 246.94 F 349.23
middle C 261.63 F# 370
C# 277.2 G 392
D 293.66 G# 415.3
APPLICATIONS
------------
The AY-3-8910/8912 (and derivatives) has found its way
into a variety of home computers and games consoles including
the following:
. Sinclair ZX Spectrum 128/+2/+3
. Amstrad CPC 464/664/6128
. Mattel Intellivision
. BBC Micro
. Atari ST
. Sega Master System
There are also a couple of emulators available at the
time of writing:
. "Z80" - the Spectrum emulator by Gerton Lunter for PCs
and compatibles which utilises the Adlib sound
generator present on most Soundblaster-compatible
cards. This package fully emulates the Spectrum 48/128
and is well worth looking at.
. "DeliAY" - by Patrik Rak for the Commodore Amiga. This
comes as an add-on for "DeliTracker" (a music player)
and emulates a Z80 and AY-3-8912 (in a Spectrum-like
fashion) giving very accurate results. A growing
number of Spectrum tunes are being gathered together
to run under this player.
ZX SPECTRUM 128 SPECIFICS
--------------------------
The Spectrum's "control" and "data" output ports are as
follows:
- control = 65533
- data = 49149
So, to produce a simple sound from BASIC...
10 LET ayctrl=65533
20 LET aydata = 49149
30 OUT ayctrl,7 : REM select the mixer register
40 OUT aydata,62 : REM enable channel A only
50 OUT ayctrl,1 : REM channel A course pitch
60 OUT aydata,50 : REM set it
70 OUT ayctrl,8 : REM channel A volume
80 OUT aydata,15 : REM set it to maximum
.... or from assembler ...
ayctrl EQU 65533
aydata EQU 49149
start ld d,7 ; select the mixer register
ld e,62 ; enable channel A only
call outer ; send it to PSG
ld d,1 ; channel A course pitch
ld e,50 ; pitch value
call outer ; send it to PSG
ld d,8 ; channel A volume
ld e,15 ; maximum
call outer ; send it to PSG
ret
outer ld bc,ayctrl ; select control port
out (c),d ; send specified value
ld bc,aydata ; select data port
out (c),e ; send specified value
ret
For an easy way to generate the required course and fine
pitch values, try the following program:
10 INPUT "Note value ",n
20 INPUT "Octave ",o
30 LET f=INT(n/2^o)
40 LET c=INT(f/256)
50 PRINT "Fine = ";f;" Course = ";c
The pitch values required by this program are as
follows:
Note Value Note Value
C 3421 F# 2419
C# 3228 G 2283
D 3047 G# 2155
D# 2876 A 2034
E 2715 A# 1920
F 2562 B 1892
REFERENCES
----------
Micro Interfacing Circuits - Book 2, by R. A. Penfold,
ISBN 0-85934-106-2
Spectrum 128 manual, (c)1986 Sinclair Research Ltd
Sinclair User magazine, 1986 (issue unknown)
This text was entered by Alastair Booker on Чth April
1995. Please feel free to contact me regarding anything
contained in this document. I have produced a generic AY-3-8912
interface circuit for Z80-based systems and will make this
available to anyone who requires it.
email: booker_a%prodev.dnet@sb.com
or : ali@tanagra.demon.co.uk
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