Another Hardware Upgrade - V9958 + OPL2 Sound

A project log for Steckschwein

A 65c02 based homebrew computer

Thomas W.Thomas W. 12/14/2018 at 16:400 Comments

Too much empty space on our new V9958 video board. So, why not add more memory? Adding another 64k maxes out the available memory for the V9958 to a whopping 192k. These additional 64k are not usable by any of the video modes directly, but are treated by the chip as so called "extended memory". Using the command engine, data can be swapped from regular video memory to extended memory or vice versa.
We decided to not use the RCA Jacks for RGB output anymore, because there was not enough space on the board edge for an extra jack for sound. Instead, we decided to go with a DIN jack. We use the same jack the NeoGeo uses for RGB, which also has a pin for audio. So one single cable to connect an RGB-Monitor. Also, there are ready made cables available. Nice.

Also, having still space to spare, we decided to add the OPL2 sound chip to the video board, too, making it a "multimedia board". The V9958 also has a pin "CPUCLK", which provides the 3,58MHz clock needed by the OPL2 chip. Sound support only existed on stripboard or even breadboard, so it really was about time.
The analog stage of the sound section by the way was closely modeled after the one in the Commodore SFX expander for the C64.

Now, only 3 boards are needed to have a full featured Steckschwein including sound.