davis@utx1.UUCP (12/16/86)
I just got my CoCo III last week and started my investigation of how it works and how it differs from the earlier models. First off, my disk controller doesn't work with it. The disk attempts to do it's thing and then fails with an I/O error. My controller is a J&M rev 1.0 with RSDOS 1.1 and works fine in my CoCo II. I called up J&M and they said for the "classic controllers", a 74LS04 chip has to be replaced with a 7404 and that they will do it for $5 + $4 shipping. I don't know the electronics reason behind this. After playing around, I did get the controller to work. All I have to do is POKE &HFFDE,0 to put it into ROM mode instead of 64K Ram mode (using CoCo II terminology). This disables the new features, but at least I can now use my disk until I get the controller fixed. The first thing I did was to start to disassemble the new code and compare the differences in the ROMs. If anybody has already done this and has a good understanding of the initialization sequence, I would like to hear from them. As far as I have gotten, these are the initialization steps (on powerup): 1. Switch into s mode that enables the initialization code which is in ROM at $C000-$FE00 (even if the disk controller is plugged in). 2. Branch to $C000 which moves a chunk of itself to $4000. 3. Branch to $4000 which does many things such as moving $E000-$FE00 to RAM, move $8000-$C000 to RAM (Extended Basic and Color Basic). If the disk controller is plugged in, it moves $C000 to $E000 to RAM. After moving the ROMs to RAM, it "modifies" the RAM versions. The mods are different for the disk, based on its version. 4. Continue with standard initialization ($A027?). There are a lot of references to address $FF90 and I don't yet know exactly what this device is yet). Maybe it is the DAT (Dynamic Address Translation) chip. ---------- Software compatibility There no longer seems to be a semi-graphics mode, so programs that use it will not be useful (independent of the monitor you are using). Some programs have title screens that were designed using semi-graphics. They will still work, but the initial display will be garbage. Sound has changed. One program I have uses 3-part music and, though distinguishable, it sounds static-y. I assume the popular 4-part music may also have this problem, though I haven't tried any. I will continue testing and would be interested in other's experiences. Gary -- Gary A. Davis Racal-Milgo P.O. Box 407044 Fort Lauderdale, Fl 33340 (305) 476-4393 ihnp4!allegra!novavax!es5vax!davis