The Hardware (Cont’d)
Contents
The Odyssey2 was based on an Intel 8048 microcontroller, a member of Intel’s MCS-48 family. This microcontroller was a “computer on a chip,” providing a CPU, 1 kB of ROM, 64 bytes of RAM, a timer, and an oscillator (clock generator) on a single chip. This made the system cheaper to build, as systems with a regular microprocessor would require these components externally. This microcontroller was clocked at 1.79 MHz and had 27 I/O lines.
In the 8048’s embedded ROM, Magnavox stored the basic code for the console to work (similar to a computer’s BIOS). Additional ROM memory was available in the game cartridges and was where the game was stored.
The graphics and sound were controlled by an Intel 8244 chip (or Intel 8245 in the European version of the Odyssey2), which was
a custom-made integrated circuit, meaning that Intel developed it exclusively for Magnavox and only sold it to this company.
The fact that the Intel 8048 microcontroller had a proprietary software burned inside it by Magnavox and the use of a proprietary audio and graphics controller, this made it impossible for other companies to clone the Odyssey2. (Cloning could be accomplished by reverse-engineering the Intel 8244 chip and creating a new chip with similar functions, but copying the contents of the 8048 internal ROM would be illegal. As far as we know, nobody cared to clone the Odyssey2.)
Additionally, the Odyssey2 had a 128-byte static RAM chip.
Figure 9: The main chips
The Intel 8244/8245 chip had a tiny embedded RAM that could store up to four programmable video objects called sprites. Each sprite measured 8 x 8 dots, meaning that each sprite occupied 64 bits, as only one color could be defined per sprite, out of eight possible colors (dark gray, red, green, orange, blue, violet, light gray, and white). Each sprite could be moved freely on the screen and could be placed side-by-side to build objects bigger than 8 x 8 dots.
Additionally, this chip had an embedded ROM with 64 pre-defined objects (i.e., sprites), such as the alphabet, symbols, numbers, and basic objects. Anyone who played on the Odyssey2 would recognize these as they would appear in several different games, such as the “tree” and “man” objects. From this library, the Odyssey2 could display up to 12 of them at the same time. This is one of the reasons why you will see several Odyssey2 games with the same look and feel. The other reason is that they were usually written by the same person or team (e.g., Ed Averett was the main programmer for the Odyssey2 and wrote 24 games himself), and they re-used parts of code that were used in one game into another.
The screen was divided into a nine columns x eight rows matrix, called a “background grid,” where each segment of each of the grid lines could be turned on or off. This grid was used to create the “maze” used in games such as K.C.’s Krazy Chase!, Turtles!, Mokeyshines!, etc. The system allowed eight different colors for the background and for the grid, plus a “light” or “dark” configuration, which added two more colors (dark blue and dark green). The colors available for the grid were black, blue, green, light green, red, violet, orange, light gray, dark blue, and dark green.
The dedicated video controller also had a collision detection system.
The audio was produced by the Intel 8244’s internal 24-bit shift register, which can use one of two frequencies (983 Hz or 3,933 Hz).
