Subject: Re: [stella] Displaying Scores From: Bill Heineman <burger@xxxxxxxxxxxxxxxxx> Date: Wed, 06 Aug 2003 09:51:01 -0700 |
on 8/5/03 9:28 PM, Brian Crawford at nastybuttr@xxxxxxxxxxx wrote: > Hi, I'm not big on programming the VCS, but I do program in other assembly > languages. I am working on a game right now, and I am interested in how 2600 > programmers display the player's score. If someone coud give me a small > routine or something like that, it would be greatly appreciated. Thanks. > The basic concept on the 2600 for scores is this. Using the BCD mode on the 6507, you store your score in a "hex" mode and use the upper 4 bits as the first digit and the lower 4 bits as the second digit. Makes converting from hex to decimal a matter of 4 LSR instrutions or an AND #$0F. Here is some code. Score DB 1 ;Current score SED ;Use BCD math CLC LDA Score ADC #$10 ;Add 10 points ADC #$22 ;Add 22 points ADC #$01 ;Add 1 point STA Score CLD ;Use binary math from now on To draw... LDA Score LSR LSR LSR LSR ; At this point A = 0 through 9 to display the score digit for the leftmost number LDA Score AND #$0F ;Now you have 0 through 9 for the rightmost digit. How you display the digit? That's another topic. Burger ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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