[Coco] HD63x09 Question

[Robert Gault]

Right, all registers and opcodes are present in either native or 6809 
emulated mode.

One thing to watch out for with the 6309 is how it handles illegal 
opcodes. The 6809 just ignores them and skips to the next instruction. 
The 6309 vectors to a bad opcode trap. If there is no trap set, it is 
never-never land. As a divide by zero is also considered in this group, 
bad math can require a reboot. So, make sure you include some type of 
error vector recovery in any code specifically for the 6309.

jdaggett at gate.net wrote:
> Roger
> 
> That is what I gathered. In "native" mode the 6309 does an 
> advanced fetch somewhat like pipelineing does. A bit of overhead 
> in internal registers and a couple of bits in the microcode to move 
> the byte through to the opcode PLA decoding circuit. Hardest part is 
> to keep track of the page2 and page3 opcodes. 
> 
> My biggest hope that the whole opcode set was avaialable in both 
> modes. I also understand that in "emmulated" mode the W register 
> is not stacked when an IRQ is envoked. The IRQ ISR will have to 
> take care of saving the contents of the W register within the ISR. 
> 
> james
> 
> On 5 Jan 2005 at 13:23, Roger Taylor wrote:
> 
> Date sent:      	Wed, 05 Jan 2005 13:23:18 -0600
> To:             	CoCoList for Color Computer Enthusiasts 
> <coco at maltedmedia.com>
> From:           	Roger Taylor <rtaylor at bayou.com>
> Subject:        	Re: [Coco] HD63x09 Question
> Send reply to:  	CoCoList for Color Computer Enthusiasts 
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> 
>>The 6809 mode is an emulation mode of the 6309.  For compatibility,
>>it's the default state the CPU starts up in.  By switching to native
>>mode, you're telling the 6309 to not try to act completely like a
>>6809, but to allow faster cycles and various other enhancements.
> 
> 
> 
>