Real-Time Clock Advancement of 2025: A Feature the VIC-20 Lacked Previously
David Hunter has created an exciting addition to the Commodore VIC-20 community, a real-time clock (RTC) add-on that brings accurate timekeeping to this classic computer. The project, showcased during the 2025 One Hertz Challenge, has been featured on Hackaday in August 2025.
The RTC add-on relies on three key components: an Arduino Uno, a Dallas DS3231 RTC module, and an IEC driver developed by Lars Pontoppidan for the MM2IEC project.
Hardware Setup
To assemble the RTC add-on, connect the Dallas DS3231 RTC module to the Arduino Uno. The Arduino then interfaces with the VIC-20 through the Commodore IEC bus, a serial interface used for peripherals.
Communication Protocol
The Arduino runs firmware that uses the IEC driver developed by Lars Pontoppidan. This driver enables the Arduino to emulate a device on the IEC bus and respond to the VIC-20’s requests, effectively reporting the current time from the DS3231 RTC module.
Software Integration
With this setup, programs written in Commodore BASIC on the VIC-20 can read the real-time clock data as if it were coming from a standard IEC device. The system is compatible with the VIC-20's IEC bus and can be chained with other peripherals like printers or disk drives.
The inspiration for this project comes from a product produced by Hayes in the 1980s, which offered a serial-port based real-time clock solution for computers without an onboard clock. David Hunter's project builds on this historical reference and demonstrates an elegant modern solution leveraging Arduino and existing IEC driver technology.
Although not extensively tested on other Commodore machines, it’s expected to work similarly on a Commodore 64. For those interested in implementing the project, detailed wiring diagrams and source code might be available through David Hunter's original project repository or the Hackaday article.
This RTC add-on provides a valuable source for real-time clock data to programs written in Commodore BASIC, making it an ideal solution for individuals who want to build clock-based projects for the VIC-20 but lack the necessary knowledge. The add-on's compatibility with the IEC bus allows it to be connected with printers, disk drives, and other devices without issues.
David Hunter's real-time clock add-on for the Commodore VIC-20 is a testament to the enduring interest in classic computers and the ingenuity of the maker community. The project invites readers to share their own nifty timekeeping projects with the community and could even inspire further exploration of real-time clock hacks for other systems, such as the Raspberry Pi.
The RTC add-on for the Commodore VIC-20, created by David Hunter, integrates hardware gadgets like the Arduino Uno, Dallas DS3231 RTC module, and an IEC driver developed for the MM2IEC project.
This technology-driven solution connects the Dallas DS3231 RTC module to the Arduino Uno, which in turn interfaces with the VIC-20 through the Commodore IEC bus.
Data-and-cloud-computing enthusiasts may find inspiration in this project, as it paves the way for potential RTC add-ons for other classic computers, such as the Raspberry Pi.
