I have a pretty good handle on the direction and data registers of the 6522. But the timers are confusing me. I read the data sheet and it talks a lot about interrupts with the timer, but code samples I've seen simply set a value in the timer and busy wait until the timer pops. In the ISR they don't do anything to service the interrupt or clear the interrupt. But when I try that I'm getting an interrupt and since my ISR doesn't clear it, I get stuck.

There's a discussion in the data sheet about control registers which might disable interrupts, but I did not quite get what they were talking about. Some code samples would be helpful, but the data sheet is lacking them.

Any pointers to code samples? Thanks in advance.

There are subtle ways an ISR or other code can clear a 6522 interrupt flag, so perhaps it's there but you don't recognize it. Simply reading some of these registers will clear the associated interrupt flag! This came up recently in connection to another topic. The attached table gives a rough idea -- HTH

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
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Take a look at the ISR and timer support in my C02 mini BIOS. It uses timer 1 for RTC and timer 2 for an accurate delay. Code is well commented and should be easy to understand. Link is here:

viewtopic.php?f=12&t=3045

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Regards, KM
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Thanks, I'll take a look later.

And make sure you go through the interrupts primer at http://wilsonminesco.com/6502interrupts/ . It also has code associated with the timers, although not all modes.

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