Programs are written in 6502 assembly, spiced with extra 65C02 opcodes and the custom instructions introduced by Hudson.
Standard Medium
Instead of relying on those chunky and boring cartridges everyone else seems to like, NEC and Hudson devised a new medium, this time with the size of a credit card, called HuCard. It was derived from an older medium called 'Bee Card', used in some MSX games.
Typical retail game.
Interestingly, they are very similar to the Sega Card, featuring 38 pins instead of 35 . Internally, however, the differences are more significant:
- The CPU memory map can access up to 1 MB of HuCard memory without a mapper, which is why the majority of games were limited to 1 MB ROMs. Even so, games like 'Street Fighter II' resided in a 2.5 MB ROM!
- There is an Audio In pin, which apparently allows the card to supply an extra audio channel.
CD-ROM Expansion
That expansion port opened the door to a wide range of accessories and expansion units, eventually transforming the simple PC Engine into something entirely different. As if that wasn't enough, the HuCard slot also complemented the possibilities of expansion. For this article, I will focus on the most notable upgrades, some of which were incorporated into later revisions of the console.
CD-ROM² Reader (TurboGrafx-16 version) . Were they in the Discman business back then?
Base required to connect the console to the reader . It also supplies power and composite video out.
How it looked with everything fitted .
Let's take a look at the CD-ROM² expansion, which consists of a CD-ROM reader and a special HuCard called the System Card. The latter acts as a BIOS to bootstrap the game and provide routines to interface with the reader. Internally, the CD-ROM reader included 64 KB of RAM for general-purpose use, another 64 KB of RAM for streaming ADPCM samples, and 2 KB for save data. As you can guess, this enabled game developers to take advantage of extra storage and CD audio, while providing publishers with the economic benefit of distributing games on a popular medium.
Years later, NEC released another CD module called the Super CD-ROM². While the reader's hardware remained mostly unchanged, its general-purpose RAM was increased to 256 KB. Customers that already owned a CD-ROM² unit could 'upgrade' it by purchasing the Super System Card, which included the additional RAM (and one more I/O routine!). On top of all that, NEC later shipped BIOS updates in the form of the Arcade Card, which now housed 2 MB of RAM.
CD-based games relied strictly on the BIOS card they were developed for, although newer cards were backwards compatible (with some exceptions). Thus, the Arcade Card became the preferred choice for users who wanted to play almost all CD-ROM-based games. I say 'almost' because third-party companies also released their own BIOS cards (e.g., the 'Games Express CD Card'), which were required to play games specifically from those studios.
With the Super CD-ROM², NEC and Hudson also shipped a new variant of the PC-Engine/TurboGrafx-16 called the Turbo Duo, which bundled the console, reader and BIOS card into a single package.
More expansions
If you are curious about other expansions, I recommend checking out the online catalogue .