MEA8000 Unknown Details

There are still a LOT of unknown details for the MEA8000. Since the chip is software programmable, it should be very easy to reverse-engineer that details - unfortunately, nobody did so, yet.

Sawtooth and/or Noise

• Theoretically, the device can output only <either> sawtooth <or> noise?
• But, some block diagrams indicate that it can output both, added together?
• Is there fade-out/fade-in switching from noise to sawtooth, or vice-versa?

Sample Rate (and related values)

• is sample rate (the actual sample output speed) 8000Hz or 8096Hz?
• if it is 8000Hz, then exact sample rate would be 3.84MHz/3/160?
• does P register overflow after 8000 or 8096 steps?
• are fm_cos and bw_exp values using divider 8000 or 8096?
• are the P and PI values in table correct (in case 8000 and 8096 are mixed)?

Filters

• is EXP formula using "-1*pi" (mess emulator) or "-2*pi" (datasheet)?

Continue Mode

• is repeated frame using FD=unchanged or FD=0 (=faster reactions)?
• is repeated frame using PI=unchanged (=can "run out of control")?

Slow-Stop Mode

• can one "resurrect" by sending data when already in "stopping" phase?
• does the hardware discard <incomplete> frames on slowstop?
• works exactly as when resending the current frame but with AMPL=0?
• are FD and PI kept unchanged?

Random Generator (Noise)

• works how exactly?

Interpolations

• does it take the whole FD period (8..64ms) to reach new target value?
• - AMPL is interpolated on the translated values (eg 0.707)?
• - FM/BW are interpolated on the COS/EXP values?

Status Register

• REQ=0 occurs for 3us after 1st..3rd Frame byte (correct)?
• REQ=0 occurs for up to 8..64ms after 4th Frame byte (really/always)?
• REQ=0 occurs for up to 8ms after Initial Pitch (really/why)?
• is it REQUIRED to send new data during ACTIVE output (to prevent slowstop)?
• is it IMPOSSIBLE to send new data during ACTIVE output (datasheet says so)?

DAC

• is there saturation occuring in case samples exceed 8bit range, and when?

Clock Source

• can be external crystal, or external TTL, or what... an external <loop>?

Specifications

• does this doc exist in internet: "MEA8000 voice synthesizer: principles and interfacing, Philips Technical Publication 101" (Philips/Elcoma 1983)?

Answer : http://zx81.ordi5.free.fr/vtr/download/MEA8000-2.pdf