The Epoch Game Pocket Computer (henceforth "Pokekon", its Japanese abbreviation*) was a handheld game system released by large Japanese toy manufacturer Epoch in 1984/85. For its time, it was quite advanced as far as videogames go, sporting a 75x64 pixel B&W dot-matrix display, interchangeable game cartridges, a circular D-pad, and six action/selection buttons.

Inevitable comparisons will be made to Milton Bradley's Microvision and Nintendo's GameBoy handhelds, as those were the major handheld systems that came before and after the Pokekon. The Pokekon trounces the Microvision in speed and specs, but that's understandable given the 5-year technological gap between them. Add another 5 years, and you'd be surprised to learn that the Pokekon compares favourably enough with Nintendo's handheld. (See specs below)

Needless to say since you've probably never heard of the Game Pocket Computer before, the Pokekon was an abject failure, and the GameBoy went on to become a massive success. It's quite a shame considering the system was powerful enough to give 1984 gamers a fun and dynamic experience. Only 5 game cartridges were made.

I had heard of the Epoch Game Pocket Computer a few months ago -- I'd heard that it wasn't the first dot-matrix handheld, but it was the first one in Japan, at least. It seemed like an intriguing and forgotten handheld system. So when I found one selling quite cheaply on Yahoo auctions in January 2008, I picked it up. Of course it is a bulky system in terms of handhelds, definitely not pocket-sized (unless you hide it in Doraemon's magic pocket, as one Japanese website put it,) but its longest side is still shorter than those of both the Microvision and massive Atari Lynx (both I and II.)

It's a shame that only 5 games were released for the Pokekon, since this is a game system, and not just some junky LSI game from the 80s or some Chinese knockoff like the Game King. The LCD screen is big enough to make games almost equal to the Gameboy -- "So why not program for it?", I said to myself. :-)

First off, then, came the usual scouring of the net for Pokekon fansites, tech sites, etc. Not a lot came up. A couple of Japanese sites had some basic information about its CPU speed, RAM, and cartridge pinout. It said the CPU was an NECμPD78c06 microcontroller, but there was almost no information about that on the web. "The Guru" had dumped in early 2007 some of the Pokekon ROMs for eventual emulation, but that's about where the work had stopped. He said that the ROMs are pin-compatible with standard EPROMs, so I removed the ROM from my Mahjongg cartridge, put a socket in its place, and dumped the Mahjongg ROM with my EPROM reader to figure out what made the games (and the system) tick.

I then went down to the nearest electronics suppliers and bought an 8K EPROM and a 32K EEPROM. The EEPROM needed a couple lines to be swapped in order to work, but it programmed and worked fine in my new dev cartridge. EEPROMs are much nicer than EPROMs for small ROM projects, because they don't need to be erased with a UV eraser for several minutes before then being programmed. They can be (re)programmed in mere minutes.

Gradually, as I modified the Mahjongg ROM and tested the EEPROM out, I figured out what a few routines did, and made up a small program to display ROM data on the Pokekon's screen. Thus, I was able to look at the Pokekon's memory map and also dump the 4K BIOS ROM internal to the 78c06 CPU. It took a bit of time to do this dumping -- visually -- but in the end the dump was successful and the checksums added up correctly.

At the same time, a few folks in the MESS development world got ahold of a disassembly of the Mahjongg game, a PDF with some instructions and info on the 78c06, and eventually, an almost full instruction list which, as it turns out, is a subset of the NEC μPD7801 CPU, a bit more common, but still pretty obscure.

Graphics are stored in 1-plane (2-colour) bitmap format and can appear anywhere in the ROM. One byte defines 8 vertical pixels, with bit 0 representing the top pixel, bit 1 representing the pixel below it, etc. The next byte defines the next 8 vertical pixels to the right of the previous byte. A set bit means that a black pixel appears at that position on the LCD, and a cleared bit means that no pixel appears (ie: white.)

Thus, when Pokekon games are viewed in a tile viewer (like YY-CHR), graphics such as the font and bitmap images appear rotated and scrambled. Setting the tile viewer's mode to Vertical rearranges them, but they are still rotated 90 degrees clockwise. The graphics have to be rotated back in order to view them in a familiar orientation. Also, whatever is black on the LCD usually appears as white in a tile viewer, so the palette needs to be adjusted accordingly.

If you want to make graphics on the Pokekon, I'd suggest you save them as 2-colour bitmaps, but also invert the colours before saving. Then import the bitmaps into a program such as YY-CHR, with the tiles set to 1-plane vertical before you do the importing. You can save the graphics to a dummy binary file so you can later insert or include the graphics in a program in the required ROM location.

A μPD7801 assembler by John Dyer. It's the only assembler I could find for this CPU family, and thus your only hope for getting your own programs onto the Game Pokekon.

As you may discover upon running it, it's a bit finicky and glitchy. All ASM code must be in UPPERCASE; labels are only distinguished by their first 6 letters, and its assembly output is not in binary, but as hex codes in ASCII. Use a hex editor (like FRHED) to import this ASCII and convert it to binary, then pad it to 4/8/16k for use in an emulator. Yeah, programming on the Pokekon is a bit of a convoluted process.

Also included in the Zip file is the opcode test asm file by the original author of the assembler, and a basic Pokekon demo asm file by me so you can see what things have to be set up in a Pokekon ROM to get it up and running.

Pokekon Cartridge Pinout.txt

Here is some data about the pin mapping of the cartridge and some PCB measurements, in case you wanted to try to make your own cart PCB.

(Sorry about the barrel distortion from my camera in these pics!)