[Coco] HD63x09 Question

[jdaggett at gate.net]

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
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From:           	Roger Taylor <rtaylor at bayou.com>
Subject:        	Re: [Coco] HD63x09 Question
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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.