Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!ihwpt!knudsen From: knudsen@ihwpt.UUCP Newsgroups: comp.sys.m6809 Subject: 2 Megabyte Coco 3 Message-ID: <1588@ihwpt.ATT.COM> Date: Fri, 10-Apr-87 15:29:45 EST Article-I.D.: ihwpt.1588 Posted: Fri Apr 10 15:29:45 1987 Date-Received: Sat, 11-Apr-87 20:07:22 EST Organization: AT&T Bell Laboratories - Naperville, Illinois Lines: 47 Keywords: Really possible, maybe easy Coco 3 Level 2 It should be possible to extend the Coco 3 to 2 Meg of RAM. It's easy for Tandy to extend the architecture itself in a redesign. It may even be possible to do it yourself with a plug-in daughter board. Reason: The GIME's DAT registers, which hold the upper addressing bits for the memory map, are defined as only 6 bits each. But they're on an 8-bit bus -- each memory address is one byte or 8 bits. So conceivably the upper 2 bits, currently unused, could also be appended to final physical addresses to get a total of 8+13 = 21 bits = 2 Meg. Not that the current hardware would do it alone. The upper two bits may not be physically implemented inside the GIME chip. Or there may be no way for them to get out as additional address bits. But of course Tandy could redesign the GIME to do this. Only one extra output pin would be needed-- it would supply a 9th address bit to the DRAMs during both RAS and CAS, which is how some 1M x 1-bit DRAMs work. (Remember the Coco3 uses two interleaved banks of 256x1 DRAMs for 512K, so 1-Meg chips would give 2 Meg). Instead of waiting for Tandy (and Social Security), someone could make a daughter board that plugs into the existing GIME socket (some plug, that) and mounts the GIME plus a few extra chips to capture the two high-order DAT bits and put them out to the other daughter board with the 16 1-Meg DRAMs. (The latter may be just the 512K board we're using today). I'm sure OS9/2 could handle the fourfold increase in RAM blocks. Right now I'm a long way from using up 512K, but hey, let's look ahead! PS: Alternately, you could use the extra two bits by right-shifting the present addresses and still have just 512K, but in smaller blocks of 2K instead of 8K. Or, 1 Meg of 4K blocks. Or 4 Meg of 16K blocks. Several tradeoffs possible.... "Don't tell me -- OS9/2 is from outer space!" "No, it's from Iowa. It just works like outer space!" -- Mike J Knudsen ...ihnp4!ihwpt!knudsen Bell Labs(AT&T) Delphi: RAGTIMER CIS: " ~E(x):[is_lunch(x) && cost(x)==0] "