Genesis:315-5685 Information

The Sega 315-5685 ASIC.

Some model 2 Genesis consoles with the VA2.3 board revision use the 315-5685 ASIC, which was manufactured by Toshiba and incorporates the VDP, I/O and bus arbiter into a single chip. This ASIC has a buggy VDP core, which mainly affects games that use raster effects or the VDP's shadow and highlight mode. Affected model 2s have the model number MK-1631A, making them easy to tell apart. The VA2 revision and VA2.3 consoles with the MK-1631 model number use the 315-5786, which fixes both the raster effects and shadow and highlight mode.

More information on these graphical effects can be found here.

Raster Effects

On the 315-5685, sprite raster effects are slightly glitched. Two examples from Castlevania Bloodlines are shown below.

On stage 2, a dark bar is visible where the reflection borders the main screen.

Shadow and Highlight Mode

This special mode can be used to either brighten or darken certain pixels, allowing for more colors than what the VDP can normally provide. On the 315-5685, shadow and highlight mode is offset by a single pixel width, leading to unusual effects. Below are a few examples, some more extreme than others. All of these screencaps were taken using the RGB output from an affected Genesis; using composite video can make some of these glitches less noticeable.

A bright "echo" appears over Mania and her reflection in Battle Mania Daiginjou.

The color bar test in the 240p Test Suite makes use of the shadow and highlight mode to display more shades, and on the 315-5685 the affected sections have a "textured" look.

Text in the Mega EverDrive Pro menu is normally in shadow and also exhibits the "echo" effect.

Red Zone has the entire playfield in shadow, which causes the targeting reticle to look blurred and a single bright vertical line to appear on the left-hand edge of the screen.

Toy Story uses the shadow and highlight mode across multiple layers on digitized stills like this, creating a very glitched appearance.