NEC PC-9801VX – Video Output

6Dec/210

NEC PC-9801VX – Video Output

After getting the PC-9801VX up and running via the monochrome output, it was time to get the RGB signals properly-connected to a real monitor. Thanks to previously playing with Amigas, I actually have an LCD on-hand that can do 15khz via a standard VGA cable. What to do? Hack together a cable that would interface with the DB-15 port on the PC-9801.

As mentioned, this unit uses a DB-15 Analog port which looks exactly like a Macintosh Video port. Of course, it's not, so you can't just use a Mac adapter, but you can refit one, thanks to this blog. You can also just roll-your-own-cable, using the pinout here. Jaycar has the necessary DB-15 male port with housing and the cable above was built.

Plugging it in saw the picture work beautifully... but the fonts were still out. A-Train was also still scaling off the bottom edge?

Front-Panel Dip-Switches

Turns out there's display configuration options on the front-panel to configure resolutions and font-sizes. As seen above, the DOS installation screen looked OK for the most part, but the selectable menu options showed stretched/cut-off fonts!? A quick read of the the dipswitch descriptions pointed to items that may help.

SW1-1 sets the output resolution from 640x200 to 640x400 and this helped a bit, but the fonts were still wrong. I then also toggled SW2-3 and SW2-4 to enable both 80-character screen width and 25-character screen height. After this? Perrrrrfect!

Very similar to the version from the MSX.

You don't have a 15khz monitor?

No fret! This is the internet and someone has already done this before. To make this work, you'll need a GBS8200 video adapter. Once you have this in-hand, you'll need to either wire things in directly, or build a circuit such as antarcticlion's GBHV_RGBS_CONV adapter. I've had a few PCBs printed for me...