airroc@pawl12.pawl.rpi.edu (Eric K Schanberger) (05/05/90)
I have a question regarding the C128's video RAM. I have read that the newer
C128D's come with 64K of it. I would like to upgrade my C128 to this
capability, because I have a program that supports it. I would like to do
this upgrade myself, but I need schematics, information, etc...perhaps
someone knows of a magazine article that details the upgrade? Any help you
can give me will be appreciated. Thanks in advance.
--
Eric K. Schanberger \ "Words are too solid - they don't move fast enough
airroc@pawl.rpi.edu \ to catch the blur in the brain that flies by and
or bitnet - \ is gone" -Suzanne Vega
usergkgw@rpitsmts.bitnet\ DISCLAIMER:"I say what I mean and I mean what I say"geoffw@xenitec.on.ca (Geoffrey Welsh) (05/06/90)
>C128D's come with 64K of it. I would like to upgrade my C128 to this >capability, because I have a program that supports it. I would like to do >this upgrade myself, but I need schematics, information, etc...perhaps >someone knows of a magazine article that details the upgrade? Any help you >can give me will be appreciated. Thanks in advance. First, I must warn you: if you haven't done a lot of printed-circuit work before (specifically, desoldering) and/or don't have the proper tools (a high-power soldering iron and a *good* solder-sucking device), you're almost sure to cause some damage to the motherboard. You have a couple of alternatives: (1) don't do it; (2) get someone who knows what they're doing to do it. Basically, you just have to replace two 4416s near the VDC with 4464 chips. This involves removing the 4416s (which are soldered to the PC board under an RF shield) without damaging the circuit traces. Since you're not going to use the 4416s for anything, you might consider using narrow-tipped snips and cutting the leads so that you can remove them one by one rather than trying to pull the chip out intact. I've also heard of a daughterboard that can be plugged into the VDC socket, but have never seen such a thing and am sure that it would be more expensive than buying a pair of 4464s (which should cost a few bucks a piece). It would also prevent you from closing the RF shield properly, but that probably doesn't bother you one bit. Once you have the 64K RAM in there, you flip a bit in the VDC to let the chip know what's there. This changes the positions of the various address lines, so the video RAM initialized in 16K mode won't give a coherent display when switched to 64K mode - you'll have to call the routines that load the character set into the VDC, but be careful that you don't just call the VDC setup routine, as that will probably reset the chip to 16K RAM mode as well. I did this modification years ago, but there wasn't much software out there that used the extra RAM. I know that a few programs do now, but I don't have a C128 anymore... <sigh> Geoff UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 My comments do not represent and should not obligate anyone but myself.