Re: [stella] Invaders Alpha 2

Subject: Re: [stella] Invaders Alpha 2
From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Fri, 18 Apr 1997 01:53:02 GMT
>I meant to add a note saying I wasn't sure which column it was because
>I couldn't count fast enough.  (The invaders kept moving. 8)  It only
>happens in one or the other, so it's probably 25.

Checking the cycle counts again, we find that the second copy of PF1 begins its
display at pixel 97 from the left edge of the screen (counting from 1), which is
97+68=pixel 165 from the leading edge of horz blank.  This means that the first
pixel of PF1 occurs during the last third of cycle 55.  In the invaders code, the
second PF1 write ended on cycle 54.. meaning there's a two-pixel (558.7
nanosecond) interval between the time at which PF1 receives new data and the time
at which the data is needed by the TIA.  Apparently, the RAM inside the TIA in
older 2600s and some 2600jrs does have a response time under 558.7 ns, but the RAM
in the TIA in your weird 2600jr and the Coleco 2600 adapter does not respond that
fast.  Very interesting.

This confirms that not all 2600s are the same, just in case we didn't know that
already =)

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