MegaReader
Inspired by Mike Gordon's SMSReader (left), I have designed and built the MegaReader (right), a similar tool.
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 holes | 1 | JP50E |
| 16V 22uF Tantalum Capacitor | 1 | WW72P |
| 35V 470uF Electrolytic Capacitor | 1 | VH47B |
| 16V 100nF Ceramic Capacitor | 5 | YR75S |
| 100V 220nF Ceramic Capacitor | 1 | RA50E |
| SIL Resistor 47K ohm | 1 | RA31J |
| 1N4001 Rectifier Diode | 1 | QL73Q |
| 7805 +5 volt regulator | 1 | QL31J |
| 4040 CMOS 12 bit binary counter IC | 2 | QW27E |
| 4019 Quad AND/OR Select Gate IC | 2 | QW17T |
| 4049 Hex Buffer Inverting IC | 1 | QX21X |
| 16 pin DIL IC socket | 5 | BL19V |
| 36 way 0.1in pitch edge connector | 2 | JB99H |
| 2.1mm power connector | 1 | RK37S |
| 25 Pin D-type right angled plug connector | 1 | FG68Y |
| 2.2k ohm metal film resistor | 3 | M2K2 |
| 100V 4.7nF Ceramic Capacitor | 3 | WX76H |
| Bell Wire | 5 | XS92A |
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
| Symbol | Meaning |
 | Break track here |
 | Solder a wire between this number and the other hole with the same number |
 | Solder a wire between this number and the same number on side A of the cartridge connector |
 | Solder a wire between this number and the same number on side B of the cartridge connector |
 | Solder a wire between here and the numbered pin on the parallel port |
 | Solder a wire between here and the positive pin of the power connector |
 | Solder a wire between here and the negative pin of the power connector |
 | SIL Resistor 47K ohm |
 | 2.2k ohm metal film resistor |
 | 16V 100nF Ceramic Capacitor |
 | 100V 4.7nF Ceramic Capacitor |
 | 35V 470uF Electrolytic Capacitor |
 | 100V 220nF Ceramic Capacitor |
 | 16V 22uF Tantalum Capacitor |
 | 7805 +5 volt regulator (I=Input, G=Ground, O=Output) |
 | 1N4001 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.