What Chips Are In the Commodore Plus/4 Computer

This article provides a technical breakdown of the specific integrated circuits that constituted the custom chipset of the Commodore Plus/4 home computer. It focuses on the unique TED architecture that replaced the widely known VIC-II and SID chips found in the Commodore 64. Readers will gain a clear understanding of the central processing unit and the multi-function chip responsible for video, sound, and input/output operations within this specific model.

The TED Architecture

The core of the Commodore Plus/4 hardware design is the TED series, which stands for Text Editing Device. This architecture was designed to be more cost-effective and integrated than the discrete chip setup of the earlier Commodore 64. The primary custom chip in this system is the MOS Technology 7360 or its later revision, the 8360. This single integrated circuit handles video display generation, sound synthesis, and system I/O, consolidating functions that were previously spread across multiple components.

The Central Processing Unit

Powering the logic and execution of commands is the MOS Technology 7501 or 8501 microprocessor. This CPU is a variant of the classic 6502 processor, optimized to work in tandem with the TED chip. While it shares the same instruction set as the processor found in the Commodore 64, the 7501 and 8501 versions were specifically packaged and timed to support the Plus/4’s memory mapping and video bandwidth requirements. The earlier production models typically feature the 7501, while later revisions utilize the 8501 for improved manufacturing efficiency.

Differences From the Commodore 64

A critical distinction in the Plus/4 chipset is the absence of the VIC-II graphics chip and the SID sound chip. Instead of the three-voice SID synthesizer, the 7360/8360 TED chip provides a simpler two-voice square wave generator with noise capabilities. Similarly, the video output is managed directly by the TED chip, which supports a palette of 121 colors but lacks the hardware sprites that made the Commodore 64 popular for gaming. This consolidation reduced the total chip count on the motherboard but also limited the machine’s multimedia capabilities compared to its predecessor.

Memory and Support Components

Surrounding the custom CPU and TED chips are standard memory integrated circuits that complete the system. The Plus/4 typically utilizes 4164 DRAM chips or later 41464 variants to provide the system’s 64 kilobytes of RAM. The system ROMs contain the Kernal operating system and the built-in Commodore 3 Plus/1 software suite. While these are not custom logic chips in the same sense as the TED or CPU, they are essential components that work alongside the custom chipset to deliver the computer’s full functionality.

Summary of Specifications

In conclusion, the Commodore Plus/4 relies on a streamlined two-chip custom solution consisting of the 7501/8501 CPU and the 7360/8360 TED chip. This combination defined the machine’s performance profile and compatibility limitations. By integrating video, audio, and I/O into the TED chip, Commodore aimed to reduce production costs, resulting in a distinct hardware identity separate from the VIC-II and SID-based systems that dominated the home computer market of the early 1980s.