How to Synthesise Music with YM 2151

Hello FPGA lovers! Today we are going to share another instalment of our YM 2151 post series.

According to the author of the original article (in Spanish), the best way to produce sound using the YM 2151 is to use the 6809 assembler which is a cross targeting assembler seen usually in Motorola and Hitachi Devices. The author has made use of a MAME or a Multiple Arcade Machine Emulator which is the best platform for recreating arcade hardware since conventional FPGA Tools are unavailable for this project (in Spanish).

The author has simulated a project in MAME and has shared the code and registry values along with its explanation. This is more than a blessing in disguise since there is very little documentation regarding the actual simulation and synthesis of sound with the YM 2151 available on the Internet.

The Registry values, name and a short description regarding the function of each register is given in a comprehensive table by the author. The most important of these registry value combinations are:

• Registry $60- $7F with Value $ 00 for volume.
• Registry $20 with value $C for Left Right output control.
• Registry $48 with value $4A for the notes and transposing it through octaves of 8 notes

Though there are a number of other registers given by the author of equal significance, the most important of these is the above quoted three registers as they play a pivotal role in sound production.

The author has also shared the asm 6809 assembler code. The table of registers executed in the code (in Spanish) can however produce a sound just once. To repeat these sounds and modulate frequencies to get a set of notes to play actual music might seem a bit tedious as there will be a need for repeated execution of the source code with some variations in registry values to produce different sounds.

By Jotego