izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh) (03/07/89)
> From: murphyjo@dekalb.UUCP (john) > Message-ID: <269@dekalb.UUCP> > 1. What besides the disk drive is different on the new system (I have > read a while back in a product reveiw that the newer machine had 64K 80-col > video RAM, instead of the 16K on the older models). I think that's it. I have no idea why Commodore didn't put 64K video RAM in the first place but, then again, I have plenty of "why didn't you do that in the first place" questions for the designers of the C128... > 3. In reguards to #1(above) how can this video RAM be accesed on the > newer model. I have an assembly routine taken from Computes book on said > older model, but I want to know if the same will work on the newer model??? Anything that will work in 16K video RAM will work with 64K. The extra memory is completely ignored on powerup in the normal C128's; the 128D may activate the 64K on powerup (if it doesn't, set bit 4 in register 28 of the VDC). Note that, when you change that bit, the meanings of all the address lines change and the data in video RAM is scrambled (including character generator info), but a quick call the the ROM routines that load that data & clear screen should fix that. After that, all normal video RAM accesses should work normally (again). The extra video RAM can be used for more character sets, more "screens" (you can now page flip through video RAM in the same way some C64 "animators" page flip the VIC sreen through normal RAM). You can also try to play with high resolution screens (the expanded memory will remove the limitation that 640 * 200 cannot be used with block colouring, etc.) although I am told that there is a bug in the VDC that prevents interlace and hi-res modes from being used at the same time (more's the pity, because that would allow 640 * 400 and perhaps slightly higher resolutions). I am told that a package called BASIC 8 will take advantage of the extra VDC RAM (I believe it supports hires graphics for the 80-column screen). =========================================================================== Internet: Geoffrey.Welsh@f171.n221.z1.fidonet.org | 66 Mooregate Crescent Usenet: watmath!isishq!izot | Suite 602 FidoNet: Geoffrey Welsh on 1:221/171 | Kitchener, Ontario PunterNet: 7/Geoffrey Welsh | N2M 5E6 CANADA BBS: (519) 742-8939 24h 7d 300/1200/2400bps | (519) 741-9553 =========================================================================== | "I don't need a disclaimer. No one pays any attention to what I say." | =========================================================================== -- Geoffrey Welsh - via FidoNet node 1:221/162 UUCP: ...!watmath!isishq!171!izot Internet: izot@f171.n221.z1.FIDONET.ORG