Re: [stella] 2600 questions

Subject: Re: [stella] 2600 questions
From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 21 Jun 2000 18:29:43 +0200
At 16:35 20.06.2000 -0700, you wrote:
> From the 2600 programmer's guide:
>"Since the TIA latches all instructions until altered by another write 
>operation it could be updated every 2 or 3 lines".
>I'm assuming this means that whenever you want the same scanline to show up 
>for multiple scanlines, you simply execute a WSYNC on the successive 
>lines?  But for any kernel that does register hits in mid-scanline, you 
>must re-execute those hits on every scanline, right?


>So if you just wanted to draw a stripe, you could have one line in the 
>kernel and all others would be WSYNCs?  Could the programmer also use this 
>screentime to perform number crunching and other non-visible stuff?  This 
>is how the paddles are typically read, correct?


>"when a 1 is written to D1 of the CTRLPF register, the left half of the 
>playfield takes on the color of player 0 and the right half takes on the 
>color of player 1."
>Does this mean it actually does a color shift automatically in 
>hardware?  Also, this feature does not prevent sprites from being used on 
>those scanlines, does it?

It uses the colour directly from the colour registers of the players.
If you change the player's colour register during display while the
playfield is drawn in this mode, the playfield changes it's colour too.

You can use the player graphics as well as the missilies, but they
would have the same colour as the playfield, so you can'd destinguish
between them and the playfield if they are drwn on top of each other.

>That's one feature I never knew about.  I thought Combat was doing the 
>color shift manually.

If you mean the score display, I think it uses the score colour mode

>Also, has anyone thought of trying to wire something into the unused bits 
>(D5 D4 and D2) of PortB/SWCHB?

Writing to two of these pins is needed to allow using both buttons on
the proline joysticks on the 7800. This isn't available in 2600 mode

Ciao, Eckhard Stolberg

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