HN613256P CM5/CM6 [Digital Percussion sound data ROM] = 256kbit (8bit x 32k) ROMs = 32 KB storage per chip

Hitachi Mask PROM, in other words it's a mass-produced fixed ROM that cannot be altered. Casio was sure those were the PCM samples they wanted and committed to having them burned permanently.

Each ROM chip holds 1.49s of sounds and can be opened as raw PCM data: signed 8-bit, mono, 20,000 Hz. Endianness does not apply to 8-bit PCM.

ROM A is CM5 which contains:
Toms 1~3, Kick, Snare, Rimshot, Closed Hi-Hat, Open Hi-Hat, and Metronome Click (in that order).

ROM B is CM6 which contains:

Clap, Ride, Cowbell, and Crash (in that order).

Aside from the binary ROMs which can be opened in Audacity, Sound Forge, or other audio editors that support raw data, the PCM data has been resaved into 44.1 kHz 32-bit WAVs for convenience, and Audacity templates with regions have also been supplied to aid in ROM editing.

The newest versions of Audacity use SoX algorithms so you should get very, very good results when resampling between 20,000 and 44,100 rates.

Standard 27C256 ROMs are pin compatible to the original chips, so just unsolder the old ROM, replace it with a socket, and then fit a 27C256 with custom sounds without any further modifications needed.
