Posted 1 month ago
Well I finally got my adapter back from Matthias (postage times are way longer during the Christmas holiday) and there was a surprise in the box! Along side my mess of wires was a nice PCB and a couple of 50 way Master System edge connectors. Matthias had taken my mess of wires and turned it into a PCB with mounting holes for both a 50 way Master System edge connector, and a 50 way Game Gear connector.
As it was not a final product, the edge of the PCB was not chamfered so I filed along the edge to make it easier to insert in to the Retrode cart slot. Next, I soldered the connectors to the board, Master System on the front, Game Gear on the back.
First off I tried a master system game (Wonder Boy). I plugged it in to the adapter which in turn I plugged into the Retrode 2. Nothing happened. I took the cart out, cleaned the contacts and tried again. Still nothing. So I tried a Game Gear game (Columns), which did exactly the same. I decided to leave it until I could email Matthias to see if I was missing something.
Before I got round to it, Matthias sent me an email to say that I would need to bridge two points on the PCB for cartridge detection to work, specifically, the two points marked with Xes (pin 19 on the Master System and a pin 32 on the PCB edge). I had noticed these when I was soldering the connectors in and wondered if something needed to be one with them. I joined the points with a length of wire and tried again. Bingo, a file appeared on screen (generic name as master system headers don’t contain the game name) which loaded in my emulator. Sorted. I guess this wire won’t be necessary when the adapters are released, the link will be added to the board.
All the Master System games I tried worked straight off, as did most of the Game Gear games, a couple needed a clean and one didn’t work at all, Fantastic dizzy. This is a Codemasters game and they used their own mapper chip which handles things differently to the Sega ones. It is documented, so maybe Matthias will be able to add compatibility in a future firmware version.
Can’t wait to see the final version of the adapters, it’s been great fun being part of the process :)
Posted 4 months ago
After my success with the Virtual Boy Retrode adapter, I decided to try making another for some of my other cartridges that weren’t already catered for. This time I opted for the Sega Master System. As Game Gear games are near enough the same as Master System games data-wise (you can play master system games on a Game Gear with a converter), I thought I would try to make a dual system adapter.
Following the same procedure as with the Virtual boy adapter, I located the Master System and Game Gear cartridge pinouts and matched them up with the relevant pins on the Mega Drive connector, first for the Master System, then for the Game Gear. There were a few differing signals, but I matched up the main ones.
Next job was to remove the ROM chip from a donor Mega Drive cartridge and start the tedious process of attaching wires to the vacant holes. I use individual strands of wire from an old Ultra DMA IDE/ATA cable for this (like the one on the left in this picture), it’s single strand and just the right thickness.
Cartridge connectors next. Master System turned out to be simple, I de-soldered an ISA card socket from an old motherboard and cut it down to size, same pin pitch and board thickness, sorted. The Game Gear proved to be more difficult. The pins on the edge of a Game Gear cartridge are arranged in offset parallel lines, so finding a suitable replacement for a real one proved to be impossible. I didn’t fancy destroying my fully working (even the sound!) Game Gear, so got a faulty one off of ebay for next to nothing and de-soldered the cartridge socket.
I soldered the Master System connector on, connected a game and plugged it in the Retrode. A quick check of the resulting file in a hex editor showed that it was reading something, and after comparing it to a reference ROM, it was almost the same, albeit with additional FF’s. This was because the Retrode is expecting 16bits of data, and the Master System is only 8bits, so the upper 8bits were empty, something for Matthias to sort in the firmware.
The Master System uses Frame Control Registers (FCR’s) to access the ROM, so the Retrode would need to be able to do the same. Matthias sent over a couple of test firmwares to try out, but unfortunately, the only cartridge we got to read correctly was Transbot, which is a 32KB cartridge, so didn’t use any FCR swapping.
Unable to resolve the issues, Matthias asked if I would be willing to send my adapter to him to continue testing, which I of course did. Now he has a working firmware, and is getting some boards made up based on my prototype! Make sure to order one when he gets them in.
Talking with Matthias before I sent off the adapter, I wondered if the Game Gear could be put on the higher 8bits of the Mega Drives 16bit data lines, enabling both Master System and Game Gear cartridges to be plugged in at the same time. He said it would be possible, but it would interfere with the auto detection. He has since mentioned that he is adding space to solder on a Game Gear cartridge connector to his adapter PCB, so hopefully he worked out a way round this. I will post the pinout for the adapter when I find out how Matthias has added the Game Gear to it.
