Re: [stella] the B. Watson's problem...

Subject: Re: [stella] the B. Watson's problem...
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Sun, 26 Aug 2001 16:13:56 -0400 (EDT)
On Fri, 24 Aug 2001, Eckhard Stolberg wrote:

> reading the timer only got me the interrupt register. Maybe I just
> mixed up the bits when I tried to transfer their address information

I think you did:

> read and clear interrupt flag: RS-, R/W, A2, A0 = 1

Ok.

> read interval timer: RS-, A4, A2, R/W, A0 = 1

read interval timer: RS-, R/W, A2 = 1:  yes, but A0 = 0
(A3 enables/disables interrupt)

> read interval timer overflow: RS-, A4, A2, R/W = 1; A0 = 0

This is the same as the corrected "read interval timer" above.

I think you just mixed up A0 for reading the timer.

In summary, if you're reading the the timer or the timer interrupt flag,
the following applies:

    RS- = 1
    R/W = 1
    A4 = don't care
    A2 = 1
    A1 = don't care

A0 chooses between reading the timer or the interrupt flag:

    if (A0 = 0) => read timer
                => A3 controls the interrupt from the timer to IRQ-
                       A3 = 0 => disables interrupt
                       A3 = 1 => enables interrupt
    if (A0 = 1) => read interrupt flag => A3 = don't care
                => A3 = don't care


-Chris


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