homebrew 'puter project

Roger Merchberger zmerch at 30below.com
Wed Nov 16 13:18:39 CST 2005


Rumor has it that Gooijen, Henk may have mentioned these words:
>... and to put oil on the fire, I am thinking about redoing the 6809 part,
>and replace it by a 68000 at 10 MHz. Maybe a single board with just
>enough I/O ports (not PIT 68230 IIRC, but simple octal latches) for
>the pdp8/e console and RAM plus EPROM on board.
>But as said: I am *thinking* about it.
>I probably first start figuring out if rewriting the pdp8/e emulator 6809
>code into 68000 assembler, making use of all the registers will give
>the speed increase to compete with the real pdp8/e.
>I have my doubts.

If you wanted to do something to make it go faster but not cause you to 
rewrite everything, you could replace the Moto6809 with a Hitachi 6309 - 
code / clock / pin compatible with the 6809, but if you set it to 
"non-compatible mode," has access to extra registers, fewer cycles for most 
instructions, not to mention a hardware divide & some 32-bit math instructions.

It'll also clock at 3 to 4 Mhz (for the CMOS part - the 63C09) so you could 
see quite a speed increase for not a lot of work...

One downfall: they ain't cheap (altho cheaper than an 8008! ;-) and can be 
tough to find if you don't know where to look. I do, tho. ;-)

Browze on over to http://www.cloud9tech.com/ - they keep 'em in stock 
there, $31 each. Great guys, and are still supporting the CoCo!

Laterz,
Roger "Merch" Merchberger

--
Roger "Merch" Merchberger   | Anarchy doesn't scale well. -- Me
zmerch at 30below.com.         |
SysAdmin, Iceberg Computers




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