Martin_H wrote:
In the ISR they don't do anything to service the interrupt or clear the interrupt.
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!
https://laughtonelectronics.com/Arcana/ ... mmary.html