CIA interrupts...

[bloodline]

When the CIA generates an interrupt, does it signal the CPU directly, or does it write to the INTREQ register?

[Toni Wilen]

INTREQ. All interrupt lines are connected to Paula. Paula sends currently active 3 bit interrupt level signal to the CPU.

[bloodline]

Great! Thanks Toni

[bloodline]

Originally Posted by Toni Wilen

INTREQ. All interrupt lines are connected to Paula. Paula sends currently active 3 bit interrupt level signal to the CPU.

So when the CPU responds to a Ports/Timer interrupt, it must both read the CIA ICR and clear the relevant bit in the INTREQ?

Also the CIA A Inmodes: I know that O2 is 10th of the 7Mhz clock, what freq is the other Mode?

[Toni Wilen]

Originally Posted by bloodline

So when the CPU responds to a Ports/Timer interrupt, it must both read the CIA ICR and clear the relevant bit in the INTREQ?

Yes, in that order or you get same interrupt twice.

[phx]

Originally Posted by bloodline

Also the CIA A Inmodes: I know that O2 is 10th of the 7Mhz clock, what freq is the other Mode?

The CIA can also count positive transitions of the CNT pin. For the CIA-A, I think CNT should be connected to the keyboard clock line, which is also used as clock for receiving key codes on the serial port.

[bloodline]

Originally Posted by phx

The CIA can also count positive transitions of the CNT pin. For the CIA-A, I think CNT should be connected to the keyboard clock line, which is also used as clock for receiving key codes on the serial port.

I forgot the keyboard would have a clock too! Cheers!