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Tindie Blog | Clockwork64: RTC for the C64! Leave a comment

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The Commodore 64 is still just as popular as ever with retro computer enthusiasts. What’s not to like? Awesome SID music, incredible demo graphics, a huge number of games (with many more being released all the time) and lots of cool peripherals to play with. One of the only areas the C64 missed out on was having a real-time clock. With the awesome Clockwork64 you can not only add an external, very accurate time display to your C64, but you can also use it in software to keep track of time.

Commodore BASIC does have a way to keep time. One of the chips has a timer in it, and increments a clock variable every 1/60th of a second. These 60ths of a second are called “jiffies” and can be accessed in a variable called TI. There’s also a formatted version of TI, simply called TI$ (TI string) which displays the jiffy count in hours, minutes and seconds. But unless TI$ is set to the current time when the machine is powered on, the user has to manually set the time, and this is lost whenever the machine is turned off. But with an external real-time clock like the Clockwork64, you can read from it using either assembly languages or PEEKs and POKEs, and set the clock accurately!

This is a really nice feature if you are using a graphical environment like GEOS, or if you’re using a terminal program that displays the current time — it’s a good way to keep track of how long you’ve been connected to your favourite BBS! Inside the Clockwork64 is the venerable DS3231 real-time clock chip from Maxim, originally made by Dallas (hence the DS prefix). These RTCs are accurate to 1 second per year, and can be calibrated if more accuracy is needed. The external 7-segment displays can show the time in different ways, from the simple HH:MM:SS to a 99-hour timer and more besides!

If you’ve ever wanted to give your C64 some accurate timekeeping and simultaneously give it some more nerd cred, make sure to check out the Clockwork64 product page — and also check out the other Commodore peripherals made by The Dark Forest!


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