Subject: Re: [stella] Okay, newbie here. . . From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx> Date: Fri, 26 Feb 1999 16:13:32 +0100 |
At 19:53 25.02.99 -0500, you wrote: >??? 1.? What does the line "org $F000" do?? It's one of the few lines >that aren't commented. It tells the assembler where to put the code. For example this is nessessary to replace labels with the actual memory address. If you have: ORG $F000 ldx #$FF LAB1: lda #$00 jmp LAB1 the assembler would know that LAB1 is at address $F002 and could replace it in the JMP command. >??? 2.? What's the difference between a "register" and an "address?" A register usually is a memory address that interfaces with some other hardware parts and makes them accessible for the programmer. For example reading from memory address $F000 will give you whatever value is stored there. Reading from memory address $0280, which is also the joystick port register, will get you the current state of the joysticks. Also the little memory inside the microprocessor, where the data gets manipulated, is called registers. >??? 3.? In Nick Bensema's "How to draw a playfield," under "Vertical >Blank," it mentions machine cycles and includes the equation >37*76=2888.? Now, my calculator says 2812 every time I punch it in.? Was >this just a typo, or am I missing something? I don't have the code here right now, but I guess that is just a little typing error on Nick's calculator. Ciao, Eckhard Stolberg -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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