Sega Master System RGB Encoder Switcher Mod Kit

Description

The world’s first encoder switcher mod kit for the Sega Master System. Finally it is possible to have a real multi-region Master System with correct colour encoding in both PAL/50Hz and NTSC/60Hz modes. Designed for those that enjoy gaming via composite video. Requires a PAL and NTSC compatible TV or upscaler as this mod creates real PAL and real NTSC to match the region of the console.

Primarily aimed at PAL Sega Master System 2 consoles with the SEGA 315-5237 IO Controller IC.

How?

It’s very simple.

1 – Re-routing clock signals

It takes the Z80 clock and the PAL subcarrier clock and sends them into a multiplexer. A switchless region mod will switch the multiplexer between these two inputs so only one is output to Pin 6 of the RGB Encoder.

2 – Inverting the region switch signal

The Master System region setting is the opposite of the RGB Encoder region setting.

CXA1145P/MB3514

• Low = PAL
• High = NTSC

The Master System

• Low = 60Hz
• High = 50Hz

Because of this the standard switch output of a Master System region mod can not switch the RGB Encoder to match the region of the console. So the mod inverts the switch signal so it can be sent to Pin 7 of the RGB Encoder.

That’s it. Just a multiplexer and an inverter.

Why?

1 – Because it was never previously possible to have a genuine PAL and a genuine NTSC Master System in one.

2 – Sometimes it’s fun to play in composite video and this means there is full compatibility with PAL and NTSC TVs.

3 – It was fun to identify a problem, study the system to try work out a solution, then design a brand new mod kit.

Requirements

1 – A way to generate a PAL and NTSC master clock such as a Dual Frequency Oscillator.

2 – A switchless region mod or a physical region switch to switch the RGB Encoder Switcher, VDP Pin 57, and DFO at the same time.

Compatibility

Compatible with the following Sega Master System consoles.

• Model 2 / PAL / 171-6395A
• Model 2 / PAL / 171-5922A

Others need to be tested but in theory it should work with any Master System that has a Z80 CPU, a SEGA 315-5237 IO IC, and a 4 pin master clock oscillator.

I am not sure how the same mod can work in an NTSC SMS console that only has a 10.7MHz crystal. There is no available PAL subcarrier frequency to make it a dual format system. More research needed.

Mod Kit Variations

There are two versions of this mod kit.

1 – A quick solder board (QSB) PCB version that solders beneath the Z80 CPU.

2 – A standard miniature PCB version which will need fully wiring. This version is intended for experimentation and checking console revision compatibility.

Availability

This is released as an open source mod kit and available to download at Github and OshPark

https://github.com/consolesunleashed/sega-master-system-rgb-encoder-switcher