6502.org

Ok, I am using a 6526 chip in my project, and I want to use a 60Hz TTL level input that is quite accurate. What would you guys recommend?

The 6526 TOD can be configured for either 50- or 60Hz input. In short, it was designed to use the line frequency to drive it (voltage dropped and signal shaped of course). As most power companies manage the number of cycles in a 24-hour period to maintain synchronous clock accuracy, it should be an accurate source.

Other than this, getting a 60Hz accurate source was accomplished by some older style chips, such as the MM5369, which uses a standard color burst Xtal at 3.58MHz. Here a link:

http://www.eleccircuit.com/60hz-clock-pulse-generator/

Yes, but that assumes using AC current as a source for the signal, but my project runs off 12v DC. I don't want to run AC just to time a chip.

I'll have a look at that pulse generator.

Re needing AC line access... true, but you never specified any details about your project. You just have to think about the options. You can also use a can oscillator and a series of dividers to get 60Hz. It all depends on your overall goals and what existing clock sources exist in your project.

You could even use the 6526's own cycle timer to trigger TOD blips.

Would vertical sync from the video be accurate enough ? It'd required a 60Hz filter.

The application will have a regulated power supply that supplies 12v and 5v DC. But no AC. The unit I'm building may also run off batteries. But I would like the TOD clock to work.

Complete 32.768 kHz can oscillators are easy to come by. Divide the output with a pair of 8 bit counters (74HC590 or equivalent) and you'll get an accurate 60 Hz square wave. It's good enough for clocks...

What would you use for your output divider value? 546.13333333333333333333333333333?

Mike B.

Barry is right there. The divisor would not be an integer if you wanted to use a 32.768 kHz signal.
You could use a 1.8432MHz crystal(an ACIA baud-rate crystal) and divide it by 30,720($7800). Or, if you're using one of the NXP UARTS, you could take the 3.6864MHz that they use and divide by 61439($EFFF). Both of those would produce 60Hz, if I've got my maths right.

A 32.768kHz oscillator was used in my first digital watch (LED), back in 1976. There was a tiny tuning thingie in there. Probably a capacitor. The clock was a bit too fast, so I connected a frequency counter and fine-tuned the 60Hz. After three months the watch was still within one second off. Presumably the oscillator had then been shifted to 32.760 kHz, which doesn't sound unreasonable.