Erik, wonderfull work. So Sprite re-definition mid-screen is possible. Fast rate video slo-mo of the screen is amazing!
The PC1 have 2 x 4416 DRAM - giving us 16KB RAM (4 x 16.384 bit x 2 chip = 16kByte), but hey we can change with 4464 and have plain 64kB!
Actually I'm trying something more complex like 640x200 x 16 color with i.e. ESP32. And unlocking also 640x400 with per-frame page change...

this utility works with dosbox ?

willow wrote on 2026-03-13, 12:35:

this utility works with dosbox ?

I'm not sure i know what util that is.

But the programs written for the PC1, does not work in DOSBox.

I have ported Styx to the Olivetti PC1. Probably the first game using the Olivettis hidden graphics mode.

Update: You can use an ordinary Atari joystick to play the game.

https://youtu.be/Z3v6KYRCbh4

AGI 16-Color Drivers for Olivetti Prodest PC1 (V6355D Hidden Mode)

I've created patched CGA overlays that give Sierra AGI v2 games true 16-color graphics on the Olivetti Prodest PC1, using the Yamaha V6355D's hidden 160×200×16 graphics mode.
Drivers available for: King's Quest I, II, III, Leisure Suit Larry, Police Quest I, Space Quest I, II

How AGI graphics work
All AGI games store their graphics as vector drawing commands and sprites using 16 EGA color indices. The AGI interpreter renders these into an internal 160×200 framebuffer with 16 colors — this is the true native resolution of all AGI graphics, regardless of adapter. On EGA, the overlay doubles each pixel horizontally to fill a 320×200 screen. On CGA, the overlay converts colors to NTSC composite artifact patterns. On the PC1, the V6355D hidden mode displays 160×200×16 natively — the exact resolution and color depth of AGI's internal framebuffer, with no pixel doubling or color reduction needed.

The CGA overlay already produces a byte format identical to V6355D's VRAM layout (4bpp packed nibbles, 80 bytes/row, interlaced banks), so the patch only changes 10 bytes — the mode register and VRAM segment. No rendering code was modified.

How to use
Copy the matching CGA_GRAF.OVL for your game version to your game disk
Run AGIPAL.COM once before launching the game — this programs the V6355D DAC with the standard 16 EGA colors. The palette is mode-independent and stays set for the entire session. We chose the EGA palette because it's the canonical palette that AGI games were designed for — every color in the game art targets these exact 16 colors.

Note on text
Game graphics look perfect — all vector art and sprites go through the overlay and display correctly in 16 colors. However, text in the status bar and dialog boxes shows some colored fringing (cyan/red pixels around character edges). This happens because the AGI interpreter draws text via INT 10h BIOS calls, which bypass the overlay and write directly to VRAM in CGA 2bpp format. Since the V6355D is in 4bpp mode, adjacent pixel pairs get merged into wrong colors at character edges. The text is fully readable — the artifacts are purely cosmetic. A fix via an INT 10h hook TSR is possible but we decided the extra complexity wasn't worth it for a cosmetic issue.

Github and download: https://github.com/RetroErik/PC1-AGI-Driver-Download

Really impressive work! Awesome to see a game from the era finally making optimal use of the capabilities of the Olivetti Prodest PC1.

People would have been blown away by this back in the 80s for sure. 😅

By the way, one additional thing to possibly play with:

If I'm not mistaken, both the Sierra and LucasArts artists were a bit frustrated by the harshness of the original CGA/Tandy/EGA 16-color palette, particularly with regards to the lack of a color that would reasonably resemble the skin color of light-skinned characters. AGI games in PCjr/Tandy and EGA modes would typically use bright red for this, but it would look a bit off. This is the reason why artists of at both these companies made extensive use of color dithering to make the most of those rigid 16 colors in later adventure games that used the full 320x200 resolution.

If I'm not mistaken, Sierra used different 16-color palettes on the Atari ST and Amiga ports of AGI adventure games for exactly this reason. Those platforms allowed the selection of 16-color palettes out of a range of 4096 colors. They took advantage of that to tweak the palettes to become more... uhm... palatable. 😉

Maybe you could experiment with making a variant of an AGI driver/patch that would pick a 16-color palette from the 512 available colors on the Olivetti Prodest PC1 that would be closer to the 16-out-of-4096 color palettes used on those other platforms?

It also makes me wonder if Sierra did anything similar when they released an MCGA-compatible version of the AGI interpreter that displayed the 16-color games in 256-color mode.

PC1PALT — TSR Palette Loader + PC1COLOR Color Finder for Olivetti Prodest PC1

UPDATED: PC1Pal v 1.0 and PC1PalT v 1.2

Two new utilities for the Olivetti Prodest PC1's Yamaha V6355D video chip:

PC1PALT is a TSR palette loader that stays resident and automatically re-applies your custom palette when games reset the CGA video mode. Switch between 10 built-in presets with live hotkeys, adjust brightness and saturation on the fly, or generate random palettes from C64, Amstrad CPC, and ZX Spectrum color pools — all while the game is running. You can also load custom palette files or specify colors by name on the command line.

This replaces the 4 CGA colors with any 4 colors from the V6355D's 512-color palette — it does not add more colors. If you want full 16-color graphics, check out the Sierra AGI overlay driver which uses the V6355D's hardware overlay to display all 16 colors simultaneously.

PC1COLOR is an interactive color finder that lets you browse all 512 colors the V6355D can produce. Handy for finding the perfect RGB values for your custom palettes.

Video of the non-TSR version: https://youtu.be/uqIDscWm9C0
Video of the TSR version for the EGA/VGA (but using it is the same for PC1) : https://youtu.be/c2lrBGcd43Q

More info, screenshots, and downloads on GitHub: https://github.com/RetroErik/PC1-Palette-Loader

I created an account just to say how happy I am to see all this new interest in the Olivetti PC1. Thank you Erik for your discoveries!
Also happy to see Simone back in the PC1 scene!

Now Adrian needs to make a more detailed video about the PC1, the American retro DOS community needs to see what this unknown machine is capable of.

Since I don’t have a mouse for the PC1 but wanted to test my new Sierra SCI0 driver with mouse support, I created a joystick‑based mouse emulator.
https://github.com/RetroErik/PC1-Labs/tree/ma … rivers/joymouse

Ok, now I must find the time to get back my PC1!

I made two new drivers for AGI and SCI Sierra adventure games for the Olivetti Prodest PC1 — in 16 colors.

AGI — a 10-byte patch to the CGA overlay. That's all it takes. The engine's internal framebuffer already matches the hidden mode exactly — 160×200 in 16 colors. The result looks like EGA.

SCI0 — a full custom driver that downsamples 320→160 in real time. With mouse support, readable text, and — somehow — 17% faster than the original CGA driver.

Together, that covers every Sierra adventure game from 1984 to 1989 — over 20 titles. King's Quest I–IV, Space Quest I–III, Police Quest 1–2, Leisure Suit Larry 1–3, and more. All running in 16 colors on a machine that was limited to four.

Video: https://youtu.be/aQYgbVWuqRI
Downloads and source: GitHub links in the video description.

If you have a PC1, give it a try — and let me know how it turns out.

Jinxter wrote on 2026-04-07, 12:34:

Since I don’t have a mouse for the PC1 but wanted to test my new Sierra SCI0 driver with mouse support, I created a joystick‑based mouse emulator.
https://github.com/RetroErik/PC1-Labs/tree/ma … rivers/joymouse

I found this picture Simone posted on the Olivetti PC1 Facebook page years ago.
You will need to get a bus quadrature mouse and rewire it, or making an adapter.

I now have a TSR called PC1-NTSC that gives CGA games 16 simultaneous colors on the PC1 by using the Yamaha V6355D's hidden 160x200x16 mode. The nice part is that this is not a software screen conversion or a per-frame copy. It works with essentially zero CPU overhead.

Why it works on the PC1:

The V6355D has a hidden 16-color graphics mode with programmable palette
The 16-color mode reads from B000h, while CGA games write to B800h
On the PC1, those addresses are mirrored to the same physical 16KB of VRAM
In that hidden mode, each 4-bit nibble is read directly as a color index
That means ordinary CGA game data can be reinterpreted directly as 16-color pixel data. For CGA mode 6, each 4-pixel pattern becomes one of the classic NTSC artifact colors. For CGA modes 4 and 5, each pixel pair becomes a blended color. So games designed for CGA composite can be shown in stable 16-color RGB on the PC1's monitor.

The TSR hooks INT 10h and automatically switches to the hidden mode when a game selects CGA mode 4, 5, or 6. It also has palette hotkeys, so you can swap between curated and reference palettes while the game is running.

I also made a video showing how it works, with game footage and an explanation of the hardware trick: https://youtu.be/P_G7ylAQ_dg
Source code / download: https://github.com/RetroErik/PC1-NTSC-Artifact-Colors

These graphics do look great! 😎
I'm glad that the V6355D gets some attention!
That enhanced CGA chip also was used in the PC/MSX hybrid "X'press 16" (aka SVI-838).

Btw, there's one thing that comes to my mind..
The MicroWeb browser has special graphics support for Amstrad/Schneider PC1512, Atari Portfolio and other vintage PCs.
Wouldn't support for Prodest PC1 be a fine addition to the list?
It's no request, I simply thought about it when watching a YT video about MicroWeb v2.