[Coco] [Color Computer] Hitachi 6309 questions

[Darren A]

On 2/11/09, David Bush wrote:
> Where can I get a 6309 upgrade pack for my 512K CoCo 3? I would like
> to be able to run it at 3.5 MHz at least, preferably 5 MHz. Can the
> CoCo memory and the rest of the motherboard handle such speeds?

There is no simple way to get a CoCo 3 to run faster than 2 MHz.  You
can take a look at this site to see one method that was used:

<http://www.axess.com/twilight/sock/4mhzproj.html>


> NitrOS-9 looks great, but there is also a lot of great CoCo software
> out there designed for RS-DOS. Specifically, Max-10 word processor,
> CoCoMax 3 graphics editor, and lots of games. I understand the 6309
> has an emulation mode versus a native mode, but how does the user
> switch between these modes? Could 6809 software inadvertently switch
> modes, resulting in possibly buggy behavior?

Mode switching is accomplished using one of the new 6309 instructions
(LDMD).  All of the new instructions and registers are available
regardless of which mode is active.  The only difference between
emulation mode and native mode is that native mode executes many
instructions in fewer clock cycles and causes the new E and F
accumulators (W) to be pushed onto the stack upon an interrupt.  There
is a second mode switch that can cause an FIRQ interrupt to push the
same set of registers as an IRQ.

Any 6809 software that executes only legal 6809 instructions should
work fine on a 6309.  Code that relies on the behavior of illegal
op-codes or invalid operands (such as in the TFR and EXG instructions)
probably won't work on a 6309.

Darren