Anyone out there have experience with an MC6821?
I am working on an upgrade project and the existing circuit uses this chip. I specifically need to determing how the IRQ lines get set active.
Thanks,
- posted
15 years ago
MC6821
Loading thread data ...
- Vote on answer
- posted
15 years ago
formatting link
- Vote on answer
- posted
15 years ago
have experience with an MC6821?
Thanks, but I have the data sheet, I just do not quite understand how the IRQ flag sets set... From readind the data sheet it appears as if the flag can be set when there is a read from a specific address, but I cannot seen to actually see this happening on a logic analyzer...
- Vote on answer
- posted
15 years ago
re have experience with an MC6821?
No, page 8 has the information you are looking for.
The interrupt is RESET when you read the peripheral data section.
The flags can not be set through the MPU data bus. They can only be set by transitions on the CA and CB peripheral control=20 pins.
Look at the information about the control register. You have to set the CA/CB pins up to generate interrupts on a H to L or=20 L to H transition and then enable the interrupt.