The AY-3-8912 Programmable Sound Generator (PSG) is a LSI Circuit which can produce a wide variety of complex sounds under software control. The AY-3-8912 is manufactured in the General Instrument N-Channel Ion Implant Process. Operation requires a single +5V power supply a TTL compatible clock, and a microprocessor controller such as the General Instrument 16-bit CP1610 or one of the PIC1650 series of 8-bit microcomputers.
The PSG is easily interfaced to any bus oriented system. Its flexibility makes it useful in applications such as music systems, sound effects generation, audible alarms, tone signalling and FSK modems. The analog sound outputs can 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 commads 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 response of the PSG ranges from sub-audible at its lowest frequency to postaudible at its highest frequency, there are a few sounds which are beyond reproduction with only the simplest electrical connections.
Since most applications of a microprecessor/PSG system would also require interfacing between outside world and the microprocessor this facility has been designed into the PSG. The AY-3-8912 has one port and 28 leads.
PIN CONFIGURATION 28 LEAD DUAL IN LINE AY-3-8912 Top View ___________________ | \___/ | ANALOG CHANNEL C -|1 28|- DA0 | | TEST 1 -|2 27|- DA1 | | Vcc (+5V) -|3 26|- DA2 | | ANALOG CHANNEL B -|4 25|- DA3 | | ANALOG CHANNEL A -|5 24|- DA4 | | Vss(GND) -|6 23|- DA5 | | IOA7 -|7 22|- DA6 | | IOA6 -|8 21|- DA7 | | IOA5 -|9 20|- BC1 | | IOA4 -|10 19|- BC2 | | IOA3 -|11 18|- BDIR | | IOA2 -|12 17|- A8 | | _____ IOA1 -|13 16|- RESET | | IOA0 -|14 15|- CLOCK |___________________| PIN FUNCTIONS DA7-DA0 (input/output/high impedance) Data/Address 7--0: pins 21--28 These 8 lines comprise the 8-bit bidirectional bus used by the microprocessor to send both data and addresses to the PSG and to recieve 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 number (0--17) and a DA7--DA4 in conjunction with address inputs A8 for high order address (chip select). A8 (input): pin 17 Address 8 These "extra" address bit is made available to enable the positioning of the PSG (assigning a 16 word memory space) in a total 512 word memory area rather than a 256 word memory area as defined by address bits DA7--DA0 alone. If the memory size does not require the use of this extra address line it may be left unconnected as it is provided with an on-chip pull-up resistor. In "noisy" environments, however, it is recommended that A8 is tied to +5V, if it is not to be used. _____ RESET (input): pin 16 For initialization/power-on purposes, applying a 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 15 This TTL-compatible input sipplies the timing reference for the Tone, Noise and Envelope Generators. BDIR, BC2, BC1 (inputs: pins 18, 19, 20 Bus DIRection, Bus Control 2, 1 These bus control signals are generated directly by the CP1610 series of microprocessors to control all external and internal bus operations in the PSG. When using a processor other than the CP1610, these signals can be provided either by comparable bus signals or by simulating the signals on I/O lines or the processor. The PSG decodes these signals as illustrated in the follwing: BDIR BC2 BC1 CP1610 PSG FUNCTION FUNCTION 0 0 0 NACT INACTIVE. See 010 (IAB). 0 0 1 ADAR LATCH ADDRESS, See 111 (INTAK). 0 1 0 IAB INACTIVE. The PSG/CPU bus is inactive DA7--DA0 are in high impedance state. 0 1 1 DTS READ FROM PSG. This signal causes the contents of the register which is currently addressed to appear on the PSG/CPU bus. DA7--DA0 are in the output mode. 1 0 0 BAR LATCH ADDRESS. See 111 (INTAK). 1 0 1 DW INACTIVE. See 010 (IAB). 1 1 0 DWS WRITE TO PSG. This signal indicates that the bus contains register data which should be latched into the currently addressed register. DA7--DA0 are in the input mode. 1 1 1 INTAK LATCH ADDRESS. This signal indicates that the bus contains a register address which should be latched in the PSG. DA7--DA0 are in input mode. While interfacing to a processor other than the CP1610 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 possible decoded 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 BC1, with BC2 tied to +5V). BDIR BC2 BC1 PSG FUNCTION 0 1 0 INACTIVE. 0 1 1 READ FROM PSG. 1 1 0 WRITE TO PSG. 1 1 1 LATCH ADDRESS. ANALOG CHANNEL A, B, C (outputs): pins 5, 4, 1 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--IOA0 (input/output): pins 7--14 Input/Output A7--A0 This parallel input/output port provides 8 bits of prarllel data to/from the PSG/CPU bus from/to any external devices connected to the IOA pins. Each pin is provided with an on-chip pull-up resistor, so that when in the "input" mode, all pins will read normally high. Therefore, the recommended method for scanning external switches would be to ground the input bit. TEST 1: pin 2 This pin is for General Instrument test purposes only and should be left open - do not use as tie-point. Vcc: pin 3 Nominal +5Volt power supply to the PSG. Vss: pin 6 Ground reference for the PSG. ARCHITECTURE The AY-3-8912 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 rigisters. Each of the 16 registers within the PSG is also readable so that the mircroprocessor can determine, as necessary, present states or stored data values. All functions of the PSG are controlled through the 16 registers which once programmed, generate and sustain the sounds, thus freeing the system processor for other tasks. REGISTER ARRAY The principle element of the PSG is the array of 16 read/write control registers. These 16 registers lock to the CPU as a block of memory and as such occupy a 16 word block out of 512 possible addresses. The 9 address bits (8 bits on the common data/address bus, and 1 separate address bit A8) are decoded as follows: ___ ___ ___ ___ ___ ___ ___ ___ ___ | | | | | | | | | | | A8|DA7|DA6|DA5|DA4|DA3|DA2|DA1|DA0| |___|___|___|___|___|___|___|___|___| | | | | | | | | | | | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |___|___|___|___|___|___|___|___|___| THRU ___ ___ ___ ___ ___ ___ ___ ___ ___ | | | | | | | | | | | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | |___|___|___|___|___|___|___|___|___| \_________________/ \_____________/ \/ \/ HIGH ORDER LOW ORDER (Chip Select) (Register No.) The four low order address bits select one of the 16 registers (R0--R15). The 5 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 buffers are forced to a high impedance state). High order address bit A8 is fixed in the PSG design to recognize a 1 code; high order address bits DA7--DA4 may be maskk-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/Decode 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. Conditioning of the Register Address Latch/Decode and Bidirectional Buffers to recognize the bus function required (anactive, latch address, write data, or read) is accomplished by the Bus Control Decode block. SOUND GENERATING BLOCKS The basic blocks in the PSG which produce the programmed sounds include: Tone Generator produce the basic square tone frequencies for each channel (A, B, C) Noise Generator produces a frequency modulated pseudo random pulse width square wave output. Mixers combine the outputs of the Tone Generators and the Noise Generator. One for each channel (A, B, C) Amplitude Control 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. Envelope Generator Produces an envelope pattern which can be used to amplitude modulate the output of each Mixer D/A Converters the three D/A Converters each produce up to a 16 level output signal as determined by the Amplitude Control I/O PORT One additional blcoks is shown in the PSG Block Diagramm which has nothing directly to do with the production of sound - this is an I/O Port (A). Since virtually all uses or 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 the 8-bit I/O Port without affecting any other function of the PSG. The I/O Port is TTL-compatible and is provided with internal pull-ups on each pin. OPERATION Since all functions of the PSG are controlled by the processor via a series of regiser 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: Operation Registers Function Tone Generator Control R0--R5 Program tone peroids. Noise Generator Control R6 Program noise peroid. Mixer Control R7 Enable tone and/or noise on selected channels. Amplitude Control R8--R10 Select "fixed" or "envelope- variable" amplitudes. Envelope Generator Control R11--R13 Program envelope period and select envelope pattern. Tone Generator Control (Registers R0, R1, R2, R3, R4, R5) The frequency of each square wave generated by the three Tone Generators (one each for Channels A, B, and C) is obtained in the PSG by first counting down the input clock by 16, the by further counting down the result by the programmed 12-bit Tone Period value. Each 12-bit value is obtained in the PSG by combining the contents of the relative Coarse and Fine Tune registers, as illustrated in the following: Coarse Tune Registers Channel Fine Tune Register R1 A R0 R3 B R2 R5 C R4 B7 B6 B5 B4 B3 B2 B1 B0 B7 B6 B5 B4 B3 B2 B1 B0 \_________/ I \ / / \/ I \ / / NOT USED I I ____________/ / / I/ ___/ TP11 TP10 TP9 TP8 TP7 TP6 TP5 TP4 TP3 TP2 TP1 TP0 12-bit Tone Period (TP) to Tone Generator 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 5-bit value consists of the lower 5-bits (B4-B0) of register R6, as illustrated in the following: Noise Period Register R6 B7 B6 B5 B4 B3 B2 B1 B0 \______/ \___________/ \/ \/ NOT USED 5-bit Noise Period (NP) to Noise Generator Mixer Control-I/O Enable (Register R7) ______ Register R7 is a multi functional Enable register which controls the three Noise/Tone Mixers and the general purpose I/O Port. 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 channel is made by the stae of bits B5-B0 or R7. The direction (input or output) of the general purpose I/O Port (IOA) is determined by the state of bit B6 or R7. These functions are illustrated in the following: Mixer Control-U/O Enable Register R7 B7 B6 B5 B4 B3 B2 B1 B0 NOT USED____/ I \______/ \______/ I __\/ \/_______ ____________ / I___________ I__________ Input Enable Noise Enable Tone Enable <-- Function I/O Port A C B A C B A <-- Channel Amplitude Control (Registers R8, R9, R10) The amplitudes of the signals generated by each of the three D/A Converters (one each for Channels A, B, and C) is determined by the contents of the lower 5 bits (B4--B0) of registers R8, R9, and R10 as illustrated in the follwing: Amplitude Control Register Channel R8 A R9 B R10 C B7 B6 B5 B4 B3 B2 B1 B0 \______/ I \________/ \/ I \/ NOT USED I L3 L2 L1 L0 I 4-bit "fixed" amplitude Level. I M amplitude "Mode" Envelope Generator Control (Registers R11, R12, R13) To accomplish the generation of fairly complex envelope patterns, two independent methods of control are provided in the PSG: first, it is possible to vary the frequency of the envelope using registers R11 and R12; and second, the relative shape and cycle pattern of the envelope can be varied using register R13. The following paragraphs explain the details of the envelope control functions, describing first the envelope period control and then the envelope shape/cycle control. ENVELOPE PERIOD CONTROL (Registers R11, R12) 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 Peroid 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: Envelope Envelope Coarse Tune Registers Fine Tune Register R12 R11 B7 B6 B5 B4 B3 B2 B1 B0 ____ B7 B6 B5 B4 B3 B2 B1 B0 / \ / I I \ / I I \ / I I \ / I TP15 TP14 TP13 TP12 TP11 TP10 TP9 TP8 TP7 TP6 TP5 TP4 TP3 TP2 TP1 TP0 16-bit Envelope Period (EP) to Envelope Generator ENVELOPE SHAPE/CYCLE CONTROL (Register R13) 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, E1, 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 R13. Each of these 4 bits controls a function in the envelope generator, as illustrated in the following: Envelope Shape/Cycle Control Register (R13) B7 B6 B5 B4 B3 B2 B1 B0 Function \_________/ I I I I_____ Hold \ \/ I I I________ Alternate I To Envelope NOT USED I I___________ Attack I Generator I______________ Continue / I/O Port Data Store (Register R14) Register R14 functions as intermediate data storage register between PSG/CPU data bus (DA0--DA7) and the I/O port (IOA7--IOA0). Using register 14 for the transfer of I/O data has no effect on sound generation. D/A Converter Operation Since the primary use of the PSG is to produce sound for the highly imperfect amplitude detection mechanism of the human ear, the D/A conversion is performed in logarithmic steps with a normalized voltage range of from 0 to 1 Volt. The specific amplitude control of each of the three D/A Converters is accomplished by the three sets of 4-bit outputs of the Amplitude Control block, while the Mixer outputs provide the base signal frequency (Noise and/or Tone).