Re: [stella] Alpha Source

Subject: Re: [stella] Alpha Source
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Wed, 17 Jan 2001 15:50:00 +0100
Hi Manuel,
in your Alpha Source you wrote

>; here's the routine
>; to convert from standard X positions to FC positions.
>; Could a good man explain me how it works?

It is basicaly doing a divsion by 15. You need this, because before hitting RESxx, normaly you are using a coarse delay loop which needs 5 cycles/loop and every cpu cycle is equal to 3 pixel (-> 3 * 5 = 15). 

The division by 15 is replaced by a divsion by 16 (you know why:) with an additional correction. Very clever!
The code returns the coarse value in Y and the fine value for HMxx in A. You can use both values directly or OR them into a single variable for later use.

Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |
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