Mhz -> MHz
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.
Various peripherals, such as the Fuller Box, use different ports to any other interface. The Fuller Box is nominally clocked at 1.75
Mhz but suffers from contention problems.
== Register map ==