neals@tekigm.UUCP (Neal Sedell) (01/22/86)
> In article <339@3comvax.UUCP> mykes@3comvax.UUCP (Mike Schwartz) writes: > >I wonder why nobody has built a 6809 card for the C64 (and C128). The > >card can't be that expensive to build, and the power of the 09 would > >make the C64 hardware do even better things than it already does. I like > >the 09 a bunch, but I don't think that the CoCo is for me (too slow, > >fair graphics, etc.). A 6809 board might even breath a lot of new life > >into the C64. There is one very good reason why nobody has built a 6809 card for the 64 similar to the CP/M card. Can you say dynamic? Normally the 6809 could have the bus when phase 2 is high, which would be wonderful. The problem is that the VIC chip needs to fetch the 40 character cell bytes once every 8 scan lines, and a couple for the sprite data, during phase 2. There are four ways to get a 6809 to wait: HALT the CPU; use the wait line (MRDY, 6809 CPU); request DMA (6809) or stop the clock (6809E CPU). None of these are compatible with the VIC scheme. The VIC chip only gives you three phase 2 cycles warning before it starts using the bus and it could take 20 cycles for the CPU to finish an instruction and HALT, MRDY has a time limit of 10 microseconds, when you request DMA you only have 15 phase 2 cycles before the CPU takes the bus back for self refresh and the returns it, and last of all the minimum clock frequency for a 6809 is 100 KHz, again limiting a delay to less than 10 microseconds. If it weren't for the VIC stealing the bus the 6809E would be almost a perfect shoe-in. It might even not need address and data buffers since it has a tristate control pin that looks like it's compatible with the specs in the 64 programmers guide, although the specs there are vary vague about the exact timing. Then again, if you blank the screen and disable the sprites the VIC chip doesn't use any phase 2 cycles, so you can have your cake, you just can't eat it :-) What about the nice CMOS 68HC09E in the latest Motorola 8-Bit uP book you ask? It didn't give any data about min clock frequency, but the Hitachi book lists preliminary specs for a 6309E (CMOS 6809E), and sorry folks, it still ain't static! :-( Then again, since someone implied the COCO is too slow, you must not be talking about using this scheme since it would be running at very nearly the same clock speed (1.0+ MHz - ~10% due to VIC accesses). If the price of 32Kx8 static rams was reasonable you could build up a little processor with it's own ram on a reasonable sized card and run it at 2 MHz. Maybe even include it's own disk controller chip. I sure wouldn't want to run OS9 from the Commiedoor disk drive! But then again you're still limited to a 40x25 screen, so why even bother with this whole thing? For fun of course! One thing I sure miss on the COCO keyboard is a lot of the "normal" keys! Take the control this/that and shove it! The $5.95 keyboards I've seen around here are almost definitely Coleco surplus and looked so humongous I don't think they would fit a COCO. Neal "why can't I get a CHEAP 6809 computer with a REAL keyboard AND expansion slot(s) INTERNAL" Sedell ...[zehntel, uw-beaver, reed, hp-pcd, hplabs, decvax]!tektronix!tekigm!neals