lechner@ucscb.UCSC.EDU (Eric Lechner) (12/08/88)
I am writing an assembly language "life" program and would like to do this:
It needs to alternate between two screens, without copying the screen (due to
time considerations. I am trying to optimize running time).
I would like to keep each screen in a different place in memory, so
that I need only change the pointer to the text screen.
I have tried the 128 programmer's reference guide, and have tried
altering location 648 (a page pointer to the top of the text screen) but
the display does not change when I change that pointer.
What am I doing wrong? Is there a pointer in the video chip that I need to
alter as well as the other pointer? Am I overlooking anything else, as well?
Any help will be appreciated.
Eric
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Eric Lechner 115 Seton Way Santa Cruz, CA 95060
lechner@ucscb.ucsc.edu ...ucbvax!ucscc!ucscb!lechnerGeoffrey.Welsh@isishq.FIDONET.ORG (Geoffrey Welsh) (12/12/88)
> From: lechner@ucscb.UCSC.EDU (Eric Lechner) > Message-ID: <5673@saturn.ucsc.edu> > I would like to keep each screen in a different place in > memory, so > that I need only change the pointer to the text screen. I assume that this is running in C64 mode? The location you mentioned (648 decimal) is for the C64 ROMs, and all it does is tell BASIC where to put the screen. If you're going to be using BASIC PRINT routines, then you'll want to update that byte, too, but the bytes you;re looking for are on the VIC chip. First of all, you'll have to set bits 1 and zero to the 16K block number that your intended screen is in. NOTE: If I rememer correctly, the character generator ROM is only visible to the VIC-II chip if its bank is set to 0 or 2 (!). If both of your screens are in the first 16K of memory, then you don;t have to worry about changing these two bits. Next you'll have to set bits 7 through 4 of the memory pointer register at $D018 to match bits 13 through 10 of the base address of your screen. Summary: Take the base address of the screen you want to display; put bits 15 and 14 of that address into bits 1 and 0 of $DD00. Put bits 13 though 10 of the address into bits 7 through 4 of $D018. That SHOULD make the VIC-II chip display your intended screen. It will not, however, update all the pointers the BASIC and KERNAL routines need to print stuff to the screen - I suggest that, if you're going to go this far you might as well do all of your own direct screen writes anyway. Geoff ( watmath!isishq!izot ) -- Geoffrey Welsh - via FidoNet node 1:221/162 UUCP: ...!watmath!isishq!Geoffrey.Welsh Internet: Geoffrey.Welsh@isishq.FIDONET.ORG
fred@cbmvax.UUCP (Fred Bowen) (12/14/88)
In article <5673@saturn.ucsc.edu> lechner@ucscb.UCSC.EDU (Eric Lechner) writes: >I am writing an assembly language "life" program and would like to do this: >It needs to alternate between two screens, without copying the screen (due to >time considerations. I am trying to optimize running time). >I would like to keep each screen in a different place in memory, so >that I need only change the pointer to the text screen. > >I have tried the 128 programmer's reference guide, and have tried >altering location 648 (a page pointer to the top of the text screen) but >the display does not change when I change that pointer. > >What am I doing wrong? Is there a pointer in the video chip that I need to >alter as well as the other pointer? Am I overlooking anything else, as well? > > Eric Lechner 115 Seton Way Santa Cruz, CA 95060 > lechner@ucscb.ucsc.edu ...ucbvax!ucscc!ucscb!lechner I don't know where you found "648"- if that's decimal, you're poking around in the C128 input buffer, and if that's hex, you're poking the VIC screen. Here's a little thing I did many, many moons ago: 0 REM ******************************* 1 REM * MOVING THE C128 TEXT SCREEN * 2 REM * * 3 REM * SCREENS MAY BE PLACED IN * <<<<<< note these conditions 4 REM * THE BITMAP RAM AREA. * 5 REM * ALL SCREENS SHARE THE SAME * 6 REM * LINE LINK TABLE AND COLOR * 7 REM * RAM. * 8 REM ******************************* 9 : 10 GRAPHIC1,1:GRAPHIC0,1:REM ALLOC RAM 12 V1=DEC("0A2C"):REM ED -> $D018 14 SP=DEC("0A3B"):REM ED SCREEN PAGE 16 TRAP9000 19 : 30 REM CLEAR AND PRINT ON EACH SCREEN 40 GOSUB100:A$="$0800":GOSUB500:SLEEP1 50 GOSUB200:A$="$2000":GOSUB500:SLEEP1 60 GOSUB300:A$="$2400":GOSUB500:SLEEP1 69 : 70 REM CYCLE THRU SCREENS 80 FORK=1TO3:ONKGOSUB100,200,300:SLEEP1:NEXT:GOTO80 99 : 100 REM NORMAL SCREEN AT $0400 120 POKEV1,DEC("14") 130 POKESP,DEC("04") 190 RETURN 199 : 200 REM ALTERNATE SCREEN AT $2000 220 POKEV1,DEC("84") 230 POKESP,DEC("20") 290 RETURN 299 : 300 REM ALTERNATE SCREEN AT $2400 320 POKEV1,DEC("94") 330 POKESP,DEC("24") 390 RETURN 399 : 500 REM PRINT TEXT ON SCREEN 510 PRINT"<^s><^q><^q>":FORK=1TO8:PRINT"<^q> THIS SCREEN IS AT "A$:NEXT 590 RETURN 599 : 9000 REM TRAP TO NORMAL SCREEN 9010 GOSUB100:TRAP:STOP -- -- -- Fred Bowen uucp: {uunet|rutgers|pyramid}!cbmvax!fred arpa: cbmvax!fred@uunet.uu.net tele: 215 431-9100 Commodore Electronics, Ltd., 1200 Wilson Drive, West Chester, PA, 19380