AY-3-8912: Difference between revisions

The '''AY-3-8912''' is a sound generator that is built-in on several 128 KB models of the [[ZX Spectrum]] and in the [[Timex 2000 series|Timex Sinclair 2068]], but can also be found in several peripherals, such as the Fuller Box an the Melodik interface. On the 128 models, it can also provide MIDI and RS-232 connections.

On [[ZX Spectrum 128K models]] the AY chip is clocked at 1.7734 MHz (to within 0.01%). Writing to port FFFDh (65533) selects a register, and reading from port FFFDh reads that register's contents. Writing to port BFFDh (49149) writes new data to the currently selected register. On the [[ZX Spectrum 128]] and [[ZX Spectrum +2]], reading from BFFDh will return the [[floating bus]] value as normal for unattached ports, but on the [[ZX Spectrum +2A/2B, +3/3B|ZX Spectrum +2A, +3, +2B, and +3B]] machines, it will return the same as reading from FFFDh. The Melodik interface uses the same ports as the Spectrum 128.

On Spectrum-based machines, the AY chip is normally clocked at half the CPU clock. Melodik, the [[Timex 2000 series|TC2068]] and the Pentagon have an AY clocked at 1.75 Mhz. The [[Timex 2000 series|TS2068]]'s AY chip is clocked at 1.764 MHz. The Timex machines use different ports to the 128.

I/O port A of the AY chip of 128K Spectrums is connected to a pair of I/O sockets, One designated RS232/MIDI and the other Keypad or Aux. Each port contains two input pins, two output pins, and 12 volt and ground rails. Communication protocols must be implemented by [[Wikipedia:Bit banging]] the pins.