VIDC Enhancer

A VIDC Enhancer is a small circuit board that allows older Archimedes models to provide a higher clock speed to the VIDC chip which provides video and audio services to the Archimedes range of computers. By driving the VIDC chip at a higher clock speed, the Archimedes is able to achieve higher screen resolutions and refresh rates that are suitable for output to a modern LCD monitor.

The VIDC Enhancer described on this page consisted of a short run being manufactured and they all found homes. Using what I'd learnt from the VIDC Enhancer project, I created a new VIDC Enhancer design called the Ultra VIDC Enhancer which delivers much more functionality and flexibility than the original design on one PCB.

Sync on Green fix

Traditionally VIDC Enhancers provide only an over-clocking function however, I resolved to create a design that would also provide a sympathetic fix to the Sync on Green bug that many older Archimedes including the A410/1 also suffer from which causes the Green element of the RGB signal to be ignored by modern monitors as can be seen in the simulated screenshot below.

Below is a photo of a real Acorn Archimedes BBC A310 using a VIDC Enhancer to display MODE 31 (800x600@16 colours) on a IIyama Prolite E430S 17" flatscreen monitor without the Sync on Green fix.

To address the Sync on Green bug, I adapted an existing VIDC Enhancer design to include a fix. The fix also provides an opportunity to draw power directly from the Archimedes motherboard instead of requiring extra power leads to be connected to the motherboard somewhere as is the method used by other VIDC Enhancers and it also solves the problem of having to find a place to securely fix the VIDC Enhancer in place.

Here's a shot of the rear of my A410/1 with the VIDC Enhancer manual override switch fitted to a spare podule opening. That particular podule has a half length Simtec IDE interface card fitted so the bottom two podules are still spare for further expansion. You can also see the 9 pin to 15 pin VGA adapter fitted to the A410/1 to present a 15-pin VGA connector to the outside world.

The end results

The result of fitting the VIDC Enhancer is that the Archimedes is able to drive the 800x600 screen resolutions at the official timing rates for the VGA standard with a refresh rate of 56Hz resulting in a very sharp, clean image as can be seen in the photo and screen shots below.

The screenshot below shows a genuine RISC OS 3.11 desktop running at 800x600 with 16 colours being produced by an Archimedes A410/1 which is made possible by the addition of the 36MHz oscillator that the VIDC Enhancer provides. You can click on the screenshot for a full size view of the desktop.

The VIDC Enhancer project page

I kept a kind of VIDC Enhancer development diary which I expanded as I went through the processes involved in designing the PCB layout and getting the board and oscillators manufactured which shows how the project came together and details some of the issues involved in creating a new VIDC Enhancer board.