Appendix B: Glossary of X65 Terms

CPU and Memory Terms

65C816 - The Western Design Center 16-bit microprocessor that serves as the CPU for the X65, offering backward compatibility with the 6502 while providing 16-bit capabilities and a 16MB address space.

Accumulator - The primary register used for arithmetic and logical operations in the 65C816 CPU.

Bank - A 64KB segment of memory in the 65C816’s address space. The X65 supports 256 banks for a total of 16MB.

Direct Page - A 256-byte region of memory that can be located anywhere in bank 0, offering faster access for certain instructions (similar to the Zero Page in 6502 processors).

Emulation Mode - A compatibility mode of the 65C816 where it behaves like a 65C02 with an 8-bit accumulator and 16-bit address space.

Native Mode - The full 16-bit operating mode of the 65C816, which the X65 uses exclusively from boot-up.

PSRAM - Pseudo Static Random-Access Memory, the type of memory used in the X65 to provide 16MB of RAM with low power consumption.

VAB (Valid Address Bus) - A signal derived from the 65C816’s VDA and VPA signals, used to optimize memory cycles when the CPU is performing internal operations.

Graphics Terms

CGIA (Color Graphics Interface Adaptor) - The X65’s graphics subsystem, combining features from Atari ANTIC and Commodore VIC-II/TED architectures.

Display List - A structured set of instructions in memory that dictates how each scanline is rendered by the CGIA.

HAM Mode (Hold-And-Modify) - A special graphics mode inspired by the Amiga that allows modifying only part of a pixel color per scan, enabling more colors per screen.

LMS (Load Memory Scan) - A display list instruction that defines the offset of display memory, holding character or tile data.

MODE7 - A chunky-pixel graphics mode with hardware-assisted affine transformations, similar to the SNES MODE7.

Multicolor Mode - A graphics mode that uses a 4-color-per-cell representation, where each byte encodes four pixels.

Sprite Multiplexing - A technique where sprite hardware is reused to display more sprites than hardware natively supports.

VPU (Video Processing Unit) - The hardware component that executes display list instructions and updates the screen accordingly.

Audio Terms

FM Synthesis - Frequency Modulation synthesis, the audio generation method used by the Yamaha SD-1 in the X65.

PWM (Pulse-Width Modulation) - A technique for generating analog signals from digital devices, used for audio generation in the X65’s dual PWM channels.

SD-1 (YMF825) - The Yamaha FM synthesizer chip used in the X65 for high-quality music synthesis.

I/O and System Terms

DE-9 - The 9-pin connector used for joystick ports in the X65, compatible with Atari-style joysticks.

DVI-D - Digital Visual Interface, the video output standard used by the X65.

ESP32-C3 - The Wi-Fi and Bluetooth module integrated into the X65.

MMIO (Memory-Mapped I/O) - A technique where hardware devices are accessed through memory addresses, used extensively in the X65.

RP2040 - The microcontroller used in the X65 to implement various peripherals and interfaces.

RP816-RIA (Retro Interface Adaptor) - The subsystem that provides USB, storage, and other modern I/O capabilities for the X65.

SPI (Serial Peripheral Interface) - A synchronous serial communication interface used for connecting various components in the X65.

UART (Universal Asynchronous Receiver/Transmitter) - A serial communication protocol used for terminal access and debugging in the X65.