leo@ihuxl.UUCP (L. H. Ringwald) (11/14/83)
Here we go again. I am looking for anyone who knows how to upgrade the CoCo-2 to 64K. I have looked breifly at the insides of one of these, and they differ substantually from the regular CoCo's. For starters, they apparently have no 12V power supplies, and therefore cannot be using 4116 RAM chips. The chips that are used are marked with in-house numbers, but by process of elimination they are probably 4516's (the most common 5V DRAMs in the D.A.T.A. books). This is nice, since the only difference in the pinout between 4516's and 4164's is A7 (which ids not connected in the 4516). The second difference is that there are no apparent jumpers. By quick (and possibly faulty) deduction, there should be two jumpers. Number 1 - the RAM size needs to be reported to the reset routine so that the SAM can be properly set up, and number 2 - there must be some way of not selecting the RAM chips if there is only 16K and an address between $4000 and $7fff is referenced. If this is not handled this address range would be aliased to the $0000 - $3fff addresses. This would fake the reset routines into thinking it has 32K RAM. Side notes - The CoCo-2 has the 1.2 Basic ROM. This ROM has a few bug fixes and a significant speed-up of BASIC. This speed-up resets from streamlining the routine that reads the keyboard. Since BASIC reads the keyboard at the end of every statement this can have a noticable impact. In fact, it speeds the execution of an empty loop by 30% (less if there is something in the loop). Some magazines have indicated that programs that jump directly to $a1c1 rather than indirectly through $a000 will not work. They will still work. The faster version resides at $a1c1, but Radio Shack/Microsoft still has $a000 pointing to the slower version. Contrary to rumour, there is no speedup poke in the new ROMS (at least none was added between 1.1 and 1.2). Leo Ringwald ihnp4!ihuxl!leo -- Leo Ringwald ihnp4!ihuxl!leo
sjt@sb6.UUCP (SIDNEY THOMPSON) (11/16/83)
The trick to the new COCO 2 is next to the PIA. I believe it is labeled W 11 and is two small feed through eylets that are filled with solder. These two should be jumpered togeather. The new COCO uses 5v only 16k chips so you simply replace them with the 64k jobbers and you are almost ready to go. Catch 22; there is no 12v power to the cartrige slot on the new COCO so you must either have the expansion box or run a HEAVY gauge wire from the power supply to the slot. The new disk controler will be a 5v only design but has not hit the street yet. Hope this is some help Sidney Thompson