MegaReader

Inspired by Mike Gordon's SMSReader (left), I have designed and built the MegaReader (right), a similar tool.

SMSReader   MegaReader

The SMSReader is an interface between a PC and a Sega Master System cartridge, which allows the contents of the cartridge to be read into the PC.

The SMS only allocates 48K of its 64K (16 bit) address space to cartridge ROM, so most games use a banking system. Banking hardware within the cartridge allows larger ROMS to be used. The SMSReader, in order to read a cartridge, thus needs to be able to write to the cartridge. Also, with a re-writable cartridge, the SMSReader can transfer data from the PC so that home-brew games and demos can be tested on a real system. The SMSReader therefore supports both reading from and writing to a cartridge.

The MegaReader is designed to perform the same job for the Sega Megadrive/Genesis system.

Since the Megadrive allocates 4MB (of 16MB) to cartridge ROM, very few cartridges use bank switching. In order to perform a read therefore, the MegaReader does not need to be able to write to the cartridge. Also, I do not have any schematics to build a re-writable cartridge for the Megadrive, so the MegaReader currently only supports reading from a cartridge.

Parts List

Description Quantity Maplin part number
Stripboard - 39 strips x 62 holes1JP50E
16V 22uF Tantalum Capacitor1WW72P
35V 470uF Electrolytic Capacitor1VH47B
16V 100nF Ceramic Capacitor5YR75S
100V 220nF Ceramic Capacitor1RA50E
SIL Resistor 47K ohm1RA31J
1N4001 Rectifier Diode1QL73Q
7805 +5 volt regulator1QL31J
4040 CMOS 12 bit binary counter IC2QW27E
4019 Quad AND/OR Select Gate IC2QW17T
4049 Hex Buffer Inverting IC1QX21X
16 pin DIL IC socket5BL19V
36 way 0.1in pitch edge connector2JB99H
2.1mm power connector1RK37S
25 Pin D-type right angled plug connector1FG68Y
2.2k ohm metal film resistor3M2K2
100V 4.7nF Ceramic Capacitor3WX76H
Bell Wire5XS92A

The megadrive uses a 64-way cartridge edge detector, but Maplin do not sell these. It is necessary to buy two 36-way connectors and cut the last 4 connections off each, then solder them to the board next to each other.

Circuit Diagram

The circuit diagram is available here. It should be the right size to print onto an A4 sheet of paper. The red crosses on the circuit diagram are places where the tracks on the underside of the board must be cut. As well as these, the tracks should be cut underneath each of the ICs and the cartridge connector, to isolate opposite pins from each other. The entire power supply section is exactly the same as that for the SMSReader. You can look at the instructions there if you are confused.

Key

SymbolMeaning
Break track hereBreak track here
Wire numberSolder a wire between this number and the other hole with the same number
Wire numberSolder a wire between this number and the same number on side A of the cartridge connector
Wire numberSolder a wire between this number and the same number on side B of the cartridge connector
Wire numberSolder a wire between here and the numbered pin on the parallel port
Wire numberSolder a wire between here and the positive pin of the power connector
Wire numberSolder a wire between here and the negative pin of the power connector
SIL Resistor 47K ohmSIL Resistor 47K ohm
2.2k ohm metal film resistor2.2k ohm metal film resistor
16V 100nF Ceramic Capacitor16V 100nF Ceramic Capacitor
100V 4.7nF Ceramic Capacitor100V 4.7nF Ceramic Capacitor
35V 470uF Electrolytic Capacitor35V 470uF Electrolytic Capacitor
100V 220nF Ceramic Capacitor100V 220nF Ceramic Capacitor
16V 22uF Tantalum Capacitor16V 22uF Tantalum Capacitor
7805 +5 volt regulator7805 +5 volt regulator (I=Input, G=Ground, O=Output)
1N4001 Rectifier Diode1N4001 Rectifier Diode

Driver

You can download the (very simple) Windows driver for the MegaReader here.

Disclaimer

This information is provided "as is", with no guarantee of correctness. I accept no responsibility for any damage or injury caused by using this information.