Pokey Anderson

POKEY, an acronym for Pot Keyboard Integrated Circuit, is a digital I/O chip designed by Doug Neubauer at Atari, Inc. for the Atari 8-bit family of home computers. It was first released with the Atari 400 and Atari 800 in 1979 and is included in all later models and the Atari 5200 console. POKEY combines functions for reading paddle controllers (potentiometers) and computer keyboards as well as sound generation and a source for pseduo-random numbers. It produces four voices of distinctive square wave audio, either as clear tones or modified with distortion settings. Neubauer also developed the Atari 8-bit killer application ''Star Raiders'' which makes use of POKEY features.

POKEY chips are used for audio in many arcade video games of the 1980s including ''Centipede'', '' Missile Command'', '' Asteroids Deluxe'', and ''Gauntlet''. Some of Atari's arcade systems use multi-core versions with 2 or 4 POKEYs in a single package for more audio channels. The Atari 7800 console allows a game cartridge to contain a POKEY, providing better sound than the system's audio chip. Only two licensed games make use of this: the ports of '' Ballblazer'' and '' Commando''.

The LSI chip has 40 pins and is identified as C012294. The USPTO granted U.S. Patent 4,314,236 to Atari on February 2, 1982 for an "Apparatus for producing a plurality of audio sound effects". The inventors listed are Steven T. Mayer and Ronald E. Milner.

No longer manufactured, POKEY is emulated in software by arcade and Atari 8-bit emulators and also via the Atari SAP music format and associated player.

Features

* Audio
** 4 semi-independent audio channels
** Channels may be configured as one of:
*** Four 8-bit channels
*** Two 16-bit channels
*** One 16-bit channel and two 8-bit channels
** Per-channel volume, frequency, and waveform (square wave with variable duty cycle or pseudorandom noise)
** 15 kHz or 64 kHz frequency divider.
** Two channels may be driven at the CPU clock frequency.
** High-pass filter
* Keyboard scan (up to 64 keys) + 2 modifier bits (Shift, Control) + Break
* Potentiometer ports (8 independent ports, each with 8-bit resolution)
* High Resolution Timers (audio channels 1, 2, and 4 can be configured to cause timer interrupts when they cross zero)
* Random number generator (8 bits of a 17-bit polynomial counter can be read)
* Serial I/O port
* Eight IRQ interrupts

Versions

By part number:
* C012294 — Used in all Atari 8-bit family computers, including the Atari XEGS, as well as the Atari 5200 console. The suffix on the chip refers to the manufacturer:
**C012294B-01 — AMI
**C012294-03 — Signetics
**C012294-19 — National Semiconductor
**C012294-22 — OKI
**C012294-31 — IMP
*137430-001 — Part number sometimes used in Atari arcade machines for POKEY.
* 137324-1221 — Quad-Core POKEY used in Atari arcade machines '' Major Havoc'', ''I, Robot'', '' Firefox'', and '' Return of the Jedi''.

Pinout

Registers

The Atari 8-bit computers map POKEY to the $D2xx_hex page and the Atari 5200 console maps it to the $E8xx_hex page.

POKEY provides 29 Read/Write registers controlling Sound, Paddle input, keyboard input, serial input/output, and interrupts. Many POKEY register addresses have dual purposes performing different functions as a Read vs a Write register. Therefore, no code should read Hardware registers expecting to retrieve the previously written value.

This problem is solved for some registers by Operating System "Shadow" registers implemented in regular RAM that mirror the values of hardware registers. During the Vertical Blank the Operating System copies the Shadow registers in RAM for Write registers to the corresponding hardware register, and updates Shadow values for Read registers from the hardware accordingly. Therefore, writes to hardware registers which have corresponding shadow registers will be overwritten by the value of the Shadow registers during the next vertical blank.

Reading values directly from hardware at an unknown stage in the display cycle may return inconsistent results (an example: reading potentiometers). Operating System Shadow registers for Read registers would usually be the preferred source of information.

Some Write hardware registers do not have corresponding Shadow registers. They can be safely written by an application without the value being overwritten during the vertical blank. If the application needs to know the last value written to the register then it is the responsibility of the application to implement its own shadow value to remember what it wrote.

In the individual register listings below the following legend applies:

Audio

Pokey contains a programmable sound generator; four audio channels with separate frequency, noise and voice level controls.

Each channel has an 8-bit frequency divider and an 8-bit register to select noise and volume.
*AUDF1 to AUDF4 – frequency register (AUDio Frequency)
*AUDC1 to AUDC4 – volume and noise register (AUDio Control)
*AUDCTL – general register, which controls generators (AUDio ConTroL)

POKEY's sound is distinctive: when the four channels are used independently, there is noticeable detuning of parts of the 12-tone equal temperament scale, due to lack of pitch accuracy. Channels may be paired for higher accuracy; in addition, multiple forms of distortion are available, allowing a thicker sound. The distortion is primarily used in music for bass parts.

One of the sound-engines developed for the Atari 8-bit family was called the AMP engine

{{Redirect category shell, ...